Heavy Fermions
We investigate the behavior of metallic compounds where the electron-electron interactions are so strong that conventional theories break down. Materials that exhibit this behavior are known as heavy fermions. We can investigate this behavior by using the nuclear spins to measure various aspects of the electrons behavior as some external parameters is tuned. For example, the coupling between the electrons is a strong function of pressure, so frequently the ground state can be adjusted by applying hydrostatic pressures on the order of 1-10 GPa (150,000 to 1,500,000 psi). Our research has focused on how the nuclear spins and their coupling to the electrons evolves under pressure.
Condensed matter scientists have a detailed understanding of the behavior of electrons in conventional metals. To lowest order one can understand several basic properties of a metal by assuming that the electrons behave independently of one another. Yet can one really expect that electrons do not interact with another, given that they are charged objects with their own magnetic moments?
In fact these electromagnetic interactions do play a big role and renomalize of the electron’s mass. For example, an electron moving through a section of Cu wire has a mass that is a few percent higher than that of a bare electron because it senses the electric and magnetic fields generated by all of the other electrons. In some well known cases, for example in platinum, the effective mass can reach as high as ten times the bare electron mass.
In a select set of metallic elements and compounds, however, the effective mass can reach up to a thousand times that of a bare electron. The interactions in these systems are so strong that the electrons can often develop new forms of collective behavior (emergence) such as superconductivity, antiferromagnetism, and other exotic forms of long range order. The superconductivity in these cases is very different from that of the conventional superconductors that were originally discovered by Kammerlingh Onnes in 1911 and are described by the Bardeen-Cooper-Schrieffer (BCS) theory.
An excellent model for heavy fermions that captures some of the essential features is the Kondo lattice, in which a set of local moments interacts magnetically with the itinerant conduction electrons. By tuning the interaction strength (J) the ground state can change from antiferromagnetic to disordered. When J is tuned just right the system undergoes a transition from long range order to disorder at T=0, undergoing a quantum phase transition. In the vicinity of this quantum critical point (QCP) the fluctuations of the system are profoundly different from those present at a conventional phase transition at finite temperature. These quantum fluctuations are believed to give rise to a plethora of novel behavior, in which the effective mass of the electrons can diverge, and the basic description of the metal (known as a Fermi liquid) breaks down entirely.
Relevant Publications
Menegasso, P.; Souza, J. C.; Vinograd, I.; Wang, Z.; Edwards, S. P.; Pagliuso, P. G.; Curro, N. J.; Urbano, R. R.
Hyperfine couplings as a probe of orbital anisotropy in heavy-fermion materials Journal Article
In: Phys. Rev. B, vol. 104, no. 3, pp. 035154, 2021.
@article{Menegasso2021b,
title = {Hyperfine couplings as a probe of orbital anisotropy in heavy-fermion materials},
author = {P. Menegasso and J. C. Souza and I. Vinograd and Z. Wang and S. P. Edwards and P. G. Pagliuso and N. J. Curro and R. R. Urbano},
doi = {10.1103/physrevb.104.035154},
year = {2021},
date = {2021-07-01},
journal = {Phys. Rev. B},
volume = {104},
number = {3},
pages = {035154},
publisher = {American Physical Society (APS)},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Lawson, M.; Bush, B. T.; Shockley, A. C.; Capan, C.; Fisk, Z.; Curro, N. J.
Site-specific Knight shift measurements of the dilute Kondo lattice system Ce$_1-x$La$_x$CoIn$_5$ Journal Article
In: Phys. Rev. B, vol. 99, no. 16, pp. 165106, 2019.
@article{Lawson2019,
title = {Site-specific Knight shift measurements of the dilute Kondo lattice system Ce$_1-x$La$_x$CoIn$_5$},
author = {M. Lawson and B. T. Bush and A. C. Shockley and C. Capan and Z. Fisk and N. J. Curro},
doi = {10.1103/physrevb.99.165106},
year = {2019},
date = {2019-04-01},
journal = {Phys. Rev. B},
volume = {99},
number = {16},
pages = {165106},
publisher = {American Physical Society (APS)},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Lawson, M.; Bush, B. T.; Kissikov, T.; Brubaker, Z.; Shirer, K. R.; Jeffries, J. R.; Ran, S.; Jeon, I.; Maple, M. B.; Curro, N. J.
Measurements of the NMR Knight shift tensor and nonlinear magnetization in URu$_2$Si$_2$ Journal Article
In: Phys. Rev. B, vol. 97, no. 7, pp. 075138, 2018.
@article{Lawson2018,
title = {Measurements of the NMR Knight shift tensor and nonlinear magnetization in URu$_2$Si$_2$},
author = {M. Lawson and B. T. Bush and T. Kissikov and Z. Brubaker and K. R. Shirer and J. R. Jeffries and S. Ran and I. Jeon and M. B. Maple and N. J. Curro},
doi = {10.1103/physrevb.97.075138},
year = {2018},
date = {2018-02-01},
urldate = {2018-02-01},
journal = {Phys. Rev. B},
volume = {97},
number = {7},
pages = {075138},
publisher = {American Physical Society (APS)},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Mendes-Santos, T.; Costa, N. C.; Batrouni, G.; Curro, N.; Santos, R. R.; Paiva, T.; Scalettar, R. T.
Impurities near an antiferromagnetic-singlet quantum critical point Journal Article
In: Phys. Rev. B, vol. 95, pp. 054419, 2017.
@article{MendesQCPimpurities,
title = {Impurities near an antiferromagnetic-singlet quantum critical point},
author = {T. Mendes-Santos and N. C. Costa and G. Batrouni and N. Curro and R. R. Santos and T. Paiva and R. T. Scalettar},
url = {http://link.aps.org/doi/10.1103/PhysRevB.95.054419},
doi = {10.1103/PhysRevB.95.054419},
year = {2017},
date = {2017-02-01},
journal = {Phys. Rev. B},
volume = {95},
pages = {054419},
publisher = {American Physical Society},
keywords = {},
pubstate = {published},
tppubtype = {article}
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Benali, A.; Bai, Z. J.; Curro, N. J.; Scalettar, R. T.
Impurity-induced antiferromagnetic domains in the periodic Anderson model Journal Article
In: Phys. Rev. B, vol. 94, pp. 085132, 2016.
@article{BenAliPAMdopants2016,
title = {Impurity-induced antiferromagnetic domains in the periodic Anderson model},
author = {A. Benali and Z. J. Bai and N. J. Curro and R. T. Scalettar},
url = {http://link.aps.org/doi/10.1103/PhysRevB.94.085132},
doi = {10.1103/PhysRevB.94.085132},
year = {2016},
date = {2016-08-01},
journal = {Phys. Rev. B},
volume = {94},
pages = {085132},
publisher = {American Physical Society},
keywords = {},
pubstate = {published},
tppubtype = {article}
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Shirer, K. R.; Dioguardi, A. P.; Bush, B. T.; Crocker, J.; Lin, C. H.; Klavins, P.; Cooley, J. C.; Maple, M. B.; Chang, K. B.; Poeppelmeier, K. R.; Curro, N. J.
$^29$Si nuclear magnetic resonance study of URu$_2$Si$_2$ under pressure Journal Article
In: Phys. B, vol. 481, pp. 232–235, 2016, ISSN: 0921-4526.
@article{ShirerURSpressure,
title = {$^29$Si nuclear magnetic resonance study of URu$_2$Si$_2$ under pressure},
author = {K. R. Shirer and A. P. Dioguardi and B. T. Bush and J. Crocker and C. H. Lin and P. Klavins and J. C. Cooley and M. B. Maple and K. B. Chang and K. R. Poeppelmeier and N. J. Curro},
url = {http://www.sciencedirect.com/science/article/pii/S0921452615303227},
doi = {10.1016/j.physb.2015.11.018},
issn = {0921-4526},
year = {2016},
date = {2016-01-01},
journal = {Phys. B},
volume = {481},
pages = {232--235},
abstract = {We report 29Si nuclear magnetic resonance measurements of single crystals and aligned powders of URu2Si2 under pressure in the hidden order and paramagnetic phases. We find that the Knight shift decreases with applied pressure, consistent with previous measurements of the static magnetic susceptibility. Previous measurements of the spin lattice relaxation time revealed a partial suppression of the density of states below 30 K. This suppression persists under pressure, and the onset temperature is mildly enhanced.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report 29Si nuclear magnetic resonance measurements of single crystals and aligned powders of URu2Si2 under pressure in the hidden order and paramagnetic phases. We find that the Knight shift decreases with applied pressure, consistent with previous measurements of the static magnetic susceptibility. Previous measurements of the spin lattice relaxation time revealed a partial suppression of the density of states below 30 K. This suppression persists under pressure, and the onset temperature is mildly enhanced.
Curro, Nicholas J
Nuclear magnetic resonance in Kondo lattice systems Journal Article
In: Rep. Prog. Phys., vol. 79, no. 6, pp. 064501, 2016.
@article{ROPP2016,
title = {Nuclear magnetic resonance in Kondo lattice systems},
author = {Nicholas J Curro},
url = {http://stacks.iop.org/0034-4885/79/i=6/a=064501},
doi = {10.1088/0034-4885/79/6/064501},
year = {2016},
date = {2016-01-01},
journal = {Rep. Prog. Phys.},
volume = {79},
number = {6},
pages = {064501},
abstract = {Nuclear magnetic resonance has emerged as a vital tool to explore the fundamental physics of Kondo lattice systems. Because nuclear spins experience two different hyperfine couplings to the itinerant conduction electrons and to the local f moments, the Knight shift can probe multiple types of spin correlations that are not accessible via other techniques. The Knight shift provides direct information about the onset of heavy electron coherence and the emergence of the heavy electron fluid.},
keywords = {},
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Nuclear magnetic resonance has emerged as a vital tool to explore the fundamental physics of Kondo lattice systems. Because nuclear spins experience two different hyperfine couplings to the itinerant conduction electrons and to the local f moments, the Knight shift can probe multiple types of spin correlations that are not accessible via other techniques. The Knight shift provides direct information about the onset of heavy electron coherence and the emergence of the heavy electron fluid.
Yang, Yi-feng; Pines, David; Curro, N. J.
Quantum critical scaling and superconductivity in heavy electron materials Journal Article
In: Phys. Rev. B, vol. 92, no. 19, pp. 195131, 2015, ISSN: 1550-235X.
@article{Yang2015,
title = {Quantum critical scaling and superconductivity in heavy electron materials},
author = {Yi-feng Yang and David Pines and N. J. Curro},
url = {http://dx.doi.org/10.1103/PhysRevB.92.195131},
doi = {10.1103/physrevb.92.195131},
issn = {1550-235X},
year = {2015},
date = {2015-11-01},
journal = {Phys. Rev. B},
volume = {92},
number = {19},
pages = {195131},
publisher = {American Physical Society (APS)},
abstract = {We use the two fluid model to determine the conditions under which the nuclear spin-lattice lattice relaxation rate T1 of candidate heavy quantum critical superconductors can exhibit scaling behavior and find that it can occur if and only if their “hidden” quantum critical spin fluctuations give rise to a temperature-independent intrinsic heavy electron spin-lattice relaxation rate. The resulting scaling of T1 with the strength of the heavy electron component and the coherence temperature T* provides a simple test for their presence at pressures at which the superconducting transition temperature Tc is maximum and is proportional to T*. These findings support the previously noted partial scaling of the spin-lattice relaxation rate with Tc in a number of important heavy electron materials and provide additional evidence that in these materials their optimal superconductivity originates in the quantum critical spin fluctuations associated with a nearby phase transition from partially localized to fully itinerant quasiparticles.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We use the two fluid model to determine the conditions under which the nuclear spin-lattice lattice relaxation rate T1 of candidate heavy quantum critical superconductors can exhibit scaling behavior and find that it can occur if and only if their “hidden” quantum critical spin fluctuations give rise to a temperature-independent intrinsic heavy electron spin-lattice relaxation rate. The resulting scaling of T1 with the strength of the heavy electron component and the coherence temperature T* provides a simple test for their presence at pressures at which the superconducting transition temperature Tc is maximum and is proportional to T*. These findings support the previously noted partial scaling of the spin-lattice relaxation rate with Tc in a number of important heavy electron materials and provide additional evidence that in these materials their optimal superconductivity originates in the quantum critical spin fluctuations associated with a nearby phase transition from partially localized to fully itinerant quasiparticles.
Lin, C. H.; Shirer, K. R.; Crocker, J.; Dioguardi, A. P.; Lawson, M. M.; Bush, B. T.; Klavins, P.; Curro, N. J.
Evolution of hyperfine parameters across a quantum critical point in CeRhIn$_5$ Journal Article
In: Phys. Rev. B, vol. 92, no. 15, pp. 155147, 2015, ISSN: 1550-235X.
@article{Lin2015,
title = {Evolution of hyperfine parameters across a quantum critical point in CeRhIn$_5$},
author = {C. H. Lin and K. R. Shirer and J. Crocker and A. P. Dioguardi and M. M. Lawson and B. T. Bush and P. Klavins and N. J. Curro},
url = {http://dx.doi.org/10.1103/PhysRevB.92.155147},
doi = {10.1103/physrevb.92.155147},
issn = {1550-235X},
year = {2015},
date = {2015-10-01},
journal = {Phys. Rev. B},
volume = {92},
number = {15},
pages = {155147},
publisher = {American Physical Society (APS)},
abstract = {We report nuclear magnetic resonance (NMR) data for both the In(1) and In(2) sites in the heavy-fermion material CeRhIn5 under hydrostatic pressure. The Knight shift data reveal a suppression of the hyperfine coupling to the In(1) site as a function of pressure, and the electric field gradient nu_alphaalpha at the In(2) site exhibits a change of slope dnu/dP at Pc1=1.75 GPa. These changes to the coupling constants reflect alterations to the electronic structure at the quantum critical point.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report nuclear magnetic resonance (NMR) data for both the In(1) and In(2) sites in the heavy-fermion material CeRhIn5 under hydrostatic pressure. The Knight shift data reveal a suppression of the hyperfine coupling to the In(1) site as a function of pressure, and the electric field gradient nu_alphaalpha at the In(2) site exhibits a change of slope dnu/dP at Pc1=1.75 GPa. These changes to the coupling constants reflect alterations to the electronic structure at the quantum critical point.
Shockley, A. C.; Shirer, K. R.; Crocker, J.; Dioguardi, A. P.; Lin, C. H.; Nisson, D. M.; apRoberts-Warren, N.; Klavins, P.; Curro, N. J.
NMR evidence of anisotropic Kondo liquid behavior in CeIrIn$_5$ Journal Article
In: Phys. Rev. B, vol. 92, no. 8, pp. 085108, 2015, ISSN: 1550-235X.
@article{Shockley2015,
title = {NMR evidence of anisotropic Kondo liquid behavior in CeIrIn$_5$},
author = {A. C. Shockley and K. R. Shirer and J. Crocker and A. P. Dioguardi and C. H. Lin and D. M. Nisson and N. apRoberts-Warren and P. Klavins and N. J. Curro},
url = {http://dx.doi.org/10.1103/PhysRevB.92.085108},
doi = {10.1103/physrevb.92.085108},
issn = {1550-235X},
year = {2015},
date = {2015-08-01},
journal = {Phys. Rev. B},
volume = {92},
number = {8},
pages = {085108},
publisher = {American Physical Society (APS)},
abstract = {We report detailed Knight-shift measurements of the two indium sites in the heavy-fermion compound CeIrIn5 as a function of temperature and field orientation. We find that the Knight-shift anomaly is orientation dependent, with a crossover temperature T* that varies by 50% as the field is rotated from (001) to (100). This result suggests that the hybridization between the Ce 4f states and the itinerant conduction electrons is anisotropic, a result that reflects its collective origin, and may lead to anisotropic Kondo liquid behavior and unconventional superconductivity.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report detailed Knight-shift measurements of the two indium sites in the heavy-fermion compound CeIrIn5 as a function of temperature and field orientation. We find that the Knight-shift anomaly is orientation dependent, with a crossover temperature T* that varies by 50% as the field is rotated from (001) to (100). This result suggests that the hybridization between the Ce 4f states and the itinerant conduction electrons is anisotropic, a result that reflects its collective origin, and may lead to anisotropic Kondo liquid behavior and unconventional superconductivity.
Seo, S.; Lu, Xin; Zhu, J-X.; Urbano, R. R.; Curro, N.; Bauer, E. D.; Sidorov, V. A.; Pham, L. D.; Park, Tuson; Fisk, Z.; Thompson, J. D.
Disorder in quantum critical superconductors Journal Article
In: Nat. Phys., vol. 10, pp. 120–125, 2014, ISSN: 1745-2481.
@article{Seo2014,
title = {Disorder in quantum critical superconductors},
author = {S. Seo and Xin Lu and J-X. Zhu and R. R. Urbano and N. Curro and E. D. Bauer and V. A. Sidorov and L. D. Pham and Tuson Park and Z. Fisk and J. D. Thompson},
url = {http://dx.doi.org/10.1038/nphys2820},
doi = {10.1038/nphys2820},
issn = {1745-2481},
year = {2014},
date = {2014-12-01},
urldate = {2014-12-01},
journal = {Nat. Phys.},
volume = {10},
pages = {120--125},
publisher = {Nature Publishing Group},
abstract = {In four classes of materials—the layered copper oxides, organics, iron pnictides and heavy-fermion compounds—an unconventional superconducting state emerges as a magnetic transition is tuned towards absolute zero temperature, that is, towards a magnetic quantum critical point1 (QCP). In most materials, the QCP is accessed by chemical substitution or applied pressure. CeCoIn5 is one of the few materials that are ‘born’ as a quantum critical superconductor2, 3, 4 and, therefore, offers the opportunity to explore the consequences of chemical disorder. Cadmium-doped crystals of CeCoIn5 are a particularly interesting case where Cd substitution induces long-range magnetic order5, as in Zn-doped copper oxides6, 7. Applied pressure globally suppresses the Cd-induced magnetic order and restores bulk superconductivity. Here we show, however, that local magnetic correlations, whose spatial extent decreases with applied pressure, persist at the extrapolated QCP. The residual droplets of impurity-induced magnetic moments prevent the reappearance of conventional signatures of quantum criticality, but induce a heterogeneous electronic state. These discoveries show that spin droplets can be a source of electronic heterogeneity and emphasize the need for caution when interpreting the effects of tuning a correlated system by chemical substitution.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In four classes of materials—the layered copper oxides, organics, iron pnictides and heavy-fermion compounds—an unconventional superconducting state emerges as a magnetic transition is tuned towards absolute zero temperature, that is, towards a magnetic quantum critical point1 (QCP). In most materials, the QCP is accessed by chemical substitution or applied pressure. CeCoIn5 is one of the few materials that are ‘born’ as a quantum critical superconductor2, 3, 4 and, therefore, offers the opportunity to explore the consequences of chemical disorder. Cadmium-doped crystals of CeCoIn5 are a particularly interesting case where Cd substitution induces long-range magnetic order5, as in Zn-doped copper oxides6, 7. Applied pressure globally suppresses the Cd-induced magnetic order and restores bulk superconductivity. Here we show, however, that local magnetic correlations, whose spatial extent decreases with applied pressure, persist at the extrapolated QCP. The residual droplets of impurity-induced magnetic moments prevent the reappearance of conventional signatures of quantum criticality, but induce a heterogeneous electronic state. These discoveries show that spin droplets can be a source of electronic heterogeneity and emphasize the need for caution when interpreting the effects of tuning a correlated system by chemical substitution.
Curro, Nicholas J
Nuclear Magnetic Resonance as a Probe of Strongly Correlated Electron Systems Book Chapter
In: Avella, Adolfo; Mancini, Ferdinando (Ed.): pp. 1–30, Springer, 2014.
@inbook{Curro2014,
title = {Nuclear Magnetic Resonance as a Probe of Strongly Correlated Electron Systems},
author = {Nicholas J Curro},
editor = {Adolfo Avella and Ferdinando Mancini},
url = {http://link.springer.com/book/10.1007/978-3-662-44133-6},
year = {2014},
date = {2014-01-01},
pages = {1--30},
publisher = {Springer},
series = {Experimental techniques for Strongly Correlated Systems},
abstract = {Beginning with the pioneering NMR experiments of Hebel and Slichter in superconducting Aluminum, nuclear magnetic resonance (NMR) has played a central role in the study of strongly correlated electron matter. The relatively small energies associated with the nuclear spin degrees of freedom guarantee that the experimental probes of the nuclear spin behavior have little or no effect on the electronic degrees of freedom. On the other hand, the hyperfine coupling between the electronic and nuclear spins enables one to probe the static and dynamic properties of the electron spins through their effect on the nuclei. NMR offers detailed microscopic information about homogeneity, dynamics, and novel phases of electron matter and can probe under extreme conditions of high magnetic field, ultra low temperature, and high pressures. This chapter discusses the basics of NMR in condensed matter solids, including basic measurements such as the Knight shift, the hyperfine field, and the relaxation rates. To illustrate these concepts we discuss the case of field-induced antiferromagnetism and the exotic superconducting phase in CeCoIn$_5$.},
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Beginning with the pioneering NMR experiments of Hebel and Slichter in superconducting Aluminum, nuclear magnetic resonance (NMR) has played a central role in the study of strongly correlated electron matter. The relatively small energies associated with the nuclear spin degrees of freedom guarantee that the experimental probes of the nuclear spin behavior have little or no effect on the electronic degrees of freedom. On the other hand, the hyperfine coupling between the electronic and nuclear spins enables one to probe the static and dynamic properties of the electron spins through their effect on the nuclei. NMR offers detailed microscopic information about homogeneity, dynamics, and novel phases of electron matter and can probe under extreme conditions of high magnetic field, ultra low temperature, and high pressures. This chapter discusses the basics of NMR in condensed matter solids, including basic measurements such as the Knight shift, the hyperfine field, and the relaxation rates. To illustrate these concepts we discuss the case of field-induced antiferromagnetism and the exotic superconducting phase in CeCoIn$_5$.
Shirer, K. R.; Haraldsen, J. T.; Dioguardi, A. P.; Crocker, J.; apRoberts-Warren, N.; Shockley, A. C.; Lin, C. -H.; Nisson, D. M.; Cooley, J. C.; Janoschek, M.; Huang, K.; Kanchanavatee, N.; Maple, M. B.; Graf, M. J.; Balatsky, A. V.; Curro, N. J.
Nuclear magnetic resonance studies of pseudospin fluctuations in URu$_2$Si$_2$ Journal Article
In: Phys. Rev. B, vol. 88, pp. 094436, 2013.
@article{ShirerURSPRB2012,
title = {Nuclear magnetic resonance studies of pseudospin fluctuations in URu$_2$Si$_2$},
author = {K. R. Shirer and J. T. Haraldsen and A. P. Dioguardi and J. Crocker and N. apRoberts-Warren and A. C. Shockley and C. -H. Lin and D. M. Nisson and J. C. Cooley and M. Janoschek and K. Huang and N. Kanchanavatee and M. B. Maple and M. J. Graf and A. V. Balatsky and N. J. Curro},
url = {http://link.aps.org/doi/10.1103/PhysRevB.88.094436},
doi = {10.1103/PhysRevB.88.094436},
year = {2013},
date = {2013-09-01},
journal = {Phys. Rev. B},
volume = {88},
pages = {094436},
publisher = {American Physical Society},
abstract = {We report 29Si nuclear magnetic resonance measurements in single crystals and aligned powders of URu2Si2 in the hidden order and paramagnetic phases. The spin-lattice relaxation data reveal evidence of pseudospin fluctuations of U moments in the paramagnetic phase. We find evidence for partial suppression of the density of states below 30 K and analyze the data in terms of a two-component spin-fermion model. We propose that this behavior is a realization of a pseudogap between the hidden-order transition THO and 30 K. This behavior is then compared to other materials that demonstrate precursor fluctuations in a pseudogap regime above a ground state with long-range order.},
keywords = {},
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We report 29Si nuclear magnetic resonance measurements in single crystals and aligned powders of URu2Si2 in the hidden order and paramagnetic phases. The spin-lattice relaxation data reveal evidence of pseudospin fluctuations of U moments in the paramagnetic phase. We find evidence for partial suppression of the density of states below 30 K and analyze the data in terms of a two-component spin-fermion model. We propose that this behavior is a realization of a pseudogap between the hidden-order transition THO and 30 K. This behavior is then compared to other materials that demonstrate precursor fluctuations in a pseudogap regime above a ground state with long-range order.
Shockley, A. C.; apRoberts-Warren, N.; Nisson, D. M.; Kuhns, P. L.; Reyes, A. P.; Yuan, S.; Curro, N. J.
NMR investigation of the Knight shift anomaly in CeIrIn$_5$ at high magnetic fields Journal Article
In: Phys. Rev. B, vol. 88, pp. 075109, 2013.
@article{CeIrIn5HighFieldNMR,
title = {NMR investigation of the Knight shift anomaly in CeIrIn$_5$ at high magnetic fields},
author = {A. C. Shockley and N. apRoberts-Warren and D. M. Nisson and P. L. Kuhns and A. P. Reyes and S. Yuan and N. J. Curro},
url = {http://link.aps.org/doi/10.1103/PhysRevB.88.075109},
doi = {10.1103/PhysRevB.88.075109},
year = {2013},
date = {2013-08-01},
journal = {Phys. Rev. B},
volume = {88},
pages = {075109},
publisher = {American Physical Society},
abstract = {We report nuclear magnetic resonance Knight shift data in the heavy-fermion material CeIrIn5 at fields up to 30 T. The Knight shift of the In displays a strong anomaly, and we analyze the results using two interpretations. We find that the Kondo lattice coherence temperature and the effective mass of the heavy electrons remain largely unaffected by the magnetic field, despite the fact that the Zeeman energy is of the order of the coherence temperature.},
keywords = {},
pubstate = {published},
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We report nuclear magnetic resonance Knight shift data in the heavy-fermion material CeIrIn5 at fields up to 30 T. The Knight shift of the In displays a strong anomaly, and we analyze the results using two interpretations. We find that the Kondo lattice coherence temperature and the effective mass of the heavy electrons remain largely unaffected by the magnetic field, despite the fact that the Zeeman energy is of the order of the coherence temperature.
Shockley, A. C.; Dioguardi, A. P.; apRoberts-Warren, N.; Klavins, P.; Capan, C.; Fisk, Z.; Curro, N. J.
Investigating the Structure of Ce$_1-x$La$_x$CoIn$_5$ Using NQR Journal Article
In: J. Supercond. Novel Magn., vol. 25, pp. 2141–2144, 2012.
@article{Shockley2012,
title = {Investigating the Structure of Ce$_1-x$La$_x$CoIn$_5$ Using NQR},
author = {A. C. Shockley and A. P. Dioguardi and N. apRoberts-Warren and P. Klavins and C. Capan and Z. Fisk and N. J. Curro},
doi = {10.1007/s10948-012-1639-5},
year = {2012},
date = {2012-01-01},
journal = {J. Supercond. Novel Magn.},
volume = {25},
pages = {2141--2144},
abstract = {We report NQR data on the heavy-fermion compound Ce x La1-x CoIn5. The NQR spectrum of the In(1) site is composed of five different peaks, which are described by a binomial distribution of the nearest-neighbor La atoms. Our results suggest that an analysis of the NQR spectra yields a more accurate doping level than energy dispersive X-ray spectroscopy (EDS) results.},
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tppubtype = {article}
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We report NQR data on the heavy-fermion compound Ce x La1-x CoIn5. The NQR spectrum of the In(1) site is composed of five different peaks, which are described by a binomial distribution of the nearest-neighbor La atoms. Our results suggest that an analysis of the NQR spectra yields a more accurate doping level than energy dispersive X-ray spectroscopy (EDS) results.
Shirer, K. R.; Shockley, A. C.; Dioguardi, A. P.; Crocker, J.; Lin, C. -H.; apRoberts-Warren, N.; Nisson, D. M.; Klavins, P.; Cooley, J. C.; Yang, Y. -F.; Curro, N. J.
Long range order and two-fluid behavior in heavy electron materials Journal Article
In: Proc. Natl. Acad. Sci., vol. 109, no. 45, pp. E3067–E3073, 2012.
@article{Shirer2012,
title = {Long range order and two-fluid behavior in heavy electron materials},
author = {K. R. Shirer and A. C. Shockley and A. P. Dioguardi and J. Crocker and C. -H. Lin and N. apRoberts-Warren and D. M. Nisson and P. Klavins and J. C. Cooley and Y. -F. Yang and N. J. Curro},
doi = {10.1073/pnas.1209609109},
year = {2012},
date = {2012-01-01},
journal = {Proc. Natl. Acad. Sci.},
volume = {109},
number = {45},
pages = {E3067--E3073},
abstract = {The heavy electron Kondo liquid is an emergent state of condensed matter that displays universal behavior independent of material details. Properties of the heavy electron liquid are best probed by NMR Knight shift measurements, which provide a direct measure of the behavior of the heavy electron liquid that emerges below the Kondo lattice coherence temperature as the lattice of local moments hybridizes with the background conduction electrons. Because the transfer of spectral weight between the localized and itinerant electronic degrees of freedom is gradual, the Kondo liquid typically coexists with the local moment component until the material orders at low temperatures. The two-fluid formula captures this behavior in a broad range of materials in the paramagnetic state. In order to investigate two-fluid behavior and the onset and physical origin of different long range ordered ground states in heavy electron materials, we have extended Knight shift measurements to URu$_2$Si$_2$, CeIrIn$_5$ and CeRhIn$_5$. In CeRhIn$_5$ we find that the antiferromagnetic order is preceded by a relocalization of the Kondo liquid, providing independent evidence for a local moment origin of antiferromagnetism. In URu$_2$Si$_2$ the hidden order is shown to emerge directly from the Kondo liquid and so is not associated with local moment physics. Our results imply that the nature of the ground state is strongly coupled with the hybridization in the Kondo lattice in agreement with phase diagram proposed by Yang and Pines.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The heavy electron Kondo liquid is an emergent state of condensed matter that displays universal behavior independent of material details. Properties of the heavy electron liquid are best probed by NMR Knight shift measurements, which provide a direct measure of the behavior of the heavy electron liquid that emerges below the Kondo lattice coherence temperature as the lattice of local moments hybridizes with the background conduction electrons. Because the transfer of spectral weight between the localized and itinerant electronic degrees of freedom is gradual, the Kondo liquid typically coexists with the local moment component until the material orders at low temperatures. The two-fluid formula captures this behavior in a broad range of materials in the paramagnetic state. In order to investigate two-fluid behavior and the onset and physical origin of different long range ordered ground states in heavy electron materials, we have extended Knight shift measurements to URu$_2$Si$_2$, CeIrIn$_5$ and CeRhIn$_5$. In CeRhIn$_5$ we find that the antiferromagnetic order is preceded by a relocalization of the Kondo liquid, providing independent evidence for a local moment origin of antiferromagnetism. In URu$_2$Si$_2$ the hidden order is shown to emerge directly from the Kondo liquid and so is not associated with local moment physics. Our results imply that the nature of the ground state is strongly coupled with the hybridization in the Kondo lattice in agreement with phase diagram proposed by Yang and Pines.
Haraldsen, J. T.; Dubi, Y.; Curro, N. J.; Balatsky, A. V.
Hidden-order pseudogap in URu$_2$Si$_2$ Journal Article
In: Phys. Rev. B, vol. 84, no. 21, pp. 214410, 2011, ISSN: 1098-0121.
@article{Haraldsen2011,
title = {Hidden-order pseudogap in URu$_2$Si$_2$},
author = {J. T. Haraldsen and Y. Dubi and N. J. Curro and A. V. Balatsky},
doi = {10.1103/PhysRevB.84.214410},
issn = {1098-0121},
year = {2011},
date = {2011-12-01},
journal = {Phys. Rev. B},
volume = {84},
number = {21},
pages = {214410},
abstract = {Through an analysis and modeling of data from various experimental techniques, we present clear evidence for the presence of a hidden-order pseudogap in URu$_2$Si$_2$ in the temperature range 25-17.5 K. Considering fluctuations of the hidden-order energy gap at the transition, we evaluate the effects that gap fluctuations would produce on observables like tunneling conductance, neutron scattering, and nuclear resonance, and relate them to the experimental findings. We show that the transition into the hidden-order phase is likely second order and is preceded by the onset of noncoherent hidden-order fluctuations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Through an analysis and modeling of data from various experimental techniques, we present clear evidence for the presence of a hidden-order pseudogap in URu$_2$Si$_2$ in the temperature range 25-17.5 K. Considering fluctuations of the hidden-order energy gap at the transition, we evaluate the effects that gap fluctuations would produce on observables like tunneling conductance, neutron scattering, and nuclear resonance, and relate them to the experimental findings. We show that the transition into the hidden-order phase is likely second order and is preceded by the onset of noncoherent hidden-order fluctuations.
Curro, Nicholas J.; Young, Ben-Li; Urbano, Ricardo R.; Graf, Matthias J.
NMR studies of field induced magnetism in CeCoIn$_5$ Journal Article
In: Phys. C, vol. 470, no. 1, SI, pp. S521–S524, 2010, ISSN: 0921-4534, (9th International Conference on Materials and Mechanisms of Superconductivity, Tokyo, Japan, SEP 07-12, 2009).
@article{Curro2010a,
title = {NMR studies of field induced magnetism in CeCoIn$_5$},
author = {Nicholas J. Curro and Ben-Li Young and Ricardo R. Urbano and Matthias J. Graf},
doi = {10.1016/j.physc.2009.10.090},
issn = {0921-4534},
year = {2010},
date = {2010-12-01},
journal = {Phys. C},
volume = {470},
number = {1, SI},
pages = {S521--S524},
abstract = {Recent Nuclear Magnetic Resonance and elastic neutron scattering experiments have revealed conclusively the presence of static incommensurate magnetism in the field-induced B phase of CeCoIn$_5$. We analyze the NMR data assuming the hyperfine coupling to the In(2) nuclei is anisotropic and simulate the spectra for several different magnetic structures. The NMR data are consistent with ordered Ce moments along the [001] direction, but are relatively insensitive to the direction of the incommensurate wavevector. (C) 2009 Published by Elsevier B.V.},
note = {9th International Conference on Materials and Mechanisms of Superconductivity, Tokyo, Japan, SEP 07-12, 2009},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recent Nuclear Magnetic Resonance and elastic neutron scattering experiments have revealed conclusively the presence of static incommensurate magnetism in the field-induced B phase of CeCoIn$_5$. We analyze the NMR data assuming the hyperfine coupling to the In(2) nuclei is anisotropic and simulate the spectra for several different magnetic structures. The NMR data are consistent with ordered Ce moments along the [001] direction, but are relatively insensitive to the direction of the incommensurate wavevector. (C) 2009 Published by Elsevier B.V.
Baek, S-H.; Curro, N. J.; Sakai, H.; Bauer, E. D.; Cooley, J. C.; Smith, J. L.
U-235 nuclear relaxation rates in an itinerant antiferromagnet USb$_2$ Journal Article
In: Phys. Rev. B, vol. 81, no. 5, pp. 054435, 2010, ISSN: 1098-0121.
@article{Baek2010,
title = {U-235 nuclear relaxation rates in an itinerant antiferromagnet USb$_2$},
author = {S-H. Baek and N. J. Curro and H. Sakai and E. D. Bauer and J. C. Cooley and J. L. Smith},
doi = {10.1103/PhysRevB.81.054435},
issn = {1098-0121},
year = {2010},
date = {2010-02-01},
journal = {Phys. Rev. B},
volume = {81},
number = {5},
pages = {054435},
abstract = {U-235 nuclear spin-lattice (T-1(-1)) and spin-spin (T-2(-1)) relaxation rates in the itinerant antiferromagnet USb2 are reported as a function of temperature in zero field. The heating effect from the intense rf pulses that are necessary for the U-235 NMR results in unusual complex thermal recovery of the nuclear magnetization which does not allow measuring T-1(-1) directly. By implementing an indirect method, however, we successfully extracted T-1(-1) of the U-235. We find that the temperature dependence of T-1(-1) for both U-235 and Sb-121 follows the power law (proportional to T-n) with the small exponent n = 0.3 suggesting that the same relaxation mechanism dominates the on-site and the ligand nuclei, but an anomaly at 5 K was observed, possibly due to the change in the transferred hyperfine coupling on the Sb site.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
U-235 nuclear spin-lattice (T-1(-1)) and spin-spin (T-2(-1)) relaxation rates in the itinerant antiferromagnet USb2 are reported as a function of temperature in zero field. The heating effect from the intense rf pulses that are necessary for the U-235 NMR results in unusual complex thermal recovery of the nuclear magnetization which does not allow measuring T-1(-1) directly. By implementing an indirect method, however, we successfully extracted T-1(-1) of the U-235. We find that the temperature dependence of T-1(-1) for both U-235 and Sb-121 follows the power law (proportional to T-n) with the small exponent n = 0.3 suggesting that the same relaxation mechanism dominates the on-site and the ligand nuclei, but an anomaly at 5 K was observed, possibly due to the change in the transferred hyperfine coupling on the Sb site.
Curro, Nicholas J.; Young, Ben-Li; Urbano, Ricardo R.; Graf, Matthias J.
Hyperfine Fields and Magnetic Structure in the B Phase of CeCoIn$_5$ Journal Article
In: J. Low Temp. Phys., vol. 158, no. 3-4, pp. 635–646, 2010, ISSN: 0022-2291.
@article{Curro2010,
title = {Hyperfine Fields and Magnetic Structure in the B Phase of CeCoIn$_5$},
author = {Nicholas J. Curro and Ben-Li Young and Ricardo R. Urbano and Matthias J. Graf},
doi = {10.1007/s10909-009-9967-y},
issn = {0022-2291},
year = {2010},
date = {2010-02-01},
journal = {J. Low Temp. Phys.},
volume = {158},
number = {3-4},
pages = {635--646},
abstract = {We re-analyze Nuclear Magnetic Resonance (NMR) spectra observed at low temperatures and high magnetic fields in the field-induced B phase of CeCoIn$_5$. The NMR spectra are consistent with incommensurate antiferromagnetic order of the Ce magnetic moments. However, we find that the spectra of the In(2) sites depend critically on the direction of the ordered moments, the ordering wavevector and the symmetry of the hyperfine coupling to the Ce spins. Assuming isotropic hyperfine coupling, the NMR spectra observed for H parallel to [100] are consistent with magnetic order with wavevector Q = pi (1+delta/a, 1/a, 1/c) and Ce moments ordered antiferromagnetically along the [100] direction in real space. If the hyperfine coupling has dipolar symmetry, then the NMR spectra require Ce moments along the [ 001] direction. The dipolar scenario is also consistent with recent neutron scattering measurements that find an ordered moment of 0.15 mu(B) along [001] and Q(n) = pi(1+delta/a, 1+delta/a, 1/c) with in-commensuration delta = 0.12 for field H parallel to [1 (1) over bar0]. Using these parameters, we find that a hyperfine field with dipolar contribution is consistent with findings from both experiments. We speculate that the B phase of CeCoIn$_5$ represents an intrinsic phase of modulated superconductivity and antiferromagnetism that can only emerge in a highly clean system.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We re-analyze Nuclear Magnetic Resonance (NMR) spectra observed at low temperatures and high magnetic fields in the field-induced B phase of CeCoIn$_5$. The NMR spectra are consistent with incommensurate antiferromagnetic order of the Ce magnetic moments. However, we find that the spectra of the In(2) sites depend critically on the direction of the ordered moments, the ordering wavevector and the symmetry of the hyperfine coupling to the Ce spins. Assuming isotropic hyperfine coupling, the NMR spectra observed for H parallel to [100] are consistent with magnetic order with wavevector Q = pi (1+delta/a, 1/a, 1/c) and Ce moments ordered antiferromagnetically along the [100] direction in real space. If the hyperfine coupling has dipolar symmetry, then the NMR spectra require Ce moments along the [ 001] direction. The dipolar scenario is also consistent with recent neutron scattering measurements that find an ordered moment of 0.15 mu(B) along [001] and Q(n) = pi(1+delta/a, 1+delta/a, 1/c) with in-commensuration delta = 0.12 for field H parallel to [1 (1) over bar0]. Using these parameters, we find that a hyperfine field with dipolar contribution is consistent with findings from both experiments. We speculate that the B phase of CeCoIn$_5$ represents an intrinsic phase of modulated superconductivity and antiferromagnetism that can only emerge in a highly clean system.
Yang, Yi-feng; Urbano, Ricardo; Curro, Nicholas J.; Pines, David; Bauer, E. D.
Magnetic Excitations in the Kondo Liquid: Superconductivity and Hidden Magnetic Quantum Critical Fluctuations Journal Article
In: Phys. Rev. Lett., vol. 103, no. 19, pp. 197004, 2009, ISSN: 0031-9007.
@article{Yang2009,
title = {Magnetic Excitations in the Kondo Liquid: Superconductivity and Hidden Magnetic Quantum Critical Fluctuations},
author = {Yi-feng Yang and Ricardo Urbano and Nicholas J. Curro and David Pines and E. D. Bauer},
doi = {10.1103/PhysRevLett.103.197004},
issn = {0031-9007},
year = {2009},
date = {2009-11-01},
journal = {Phys. Rev. Lett.},
volume = {103},
number = {19},
pages = {197004},
abstract = {We report Knight-shift experiments on the superconducting heavy-electron material CeCoIn(5) that allow one to track with some precision the behavior of the heavy-electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the (115)In nuclear quadrupole resonance spin-lattice relaxation rate T(1)(-1) measurements under pressure reveals the presence of 2d magnetic quantum critical fluctuations in the heavy-electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point located at slightly negative pressure in CeCoIn(5) and provide additional evidence for significant similarities between the heavy-electron materials and the high-T(c) cuprates.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report Knight-shift experiments on the superconducting heavy-electron material CeCoIn(5) that allow one to track with some precision the behavior of the heavy-electron Kondo liquid in the superconducting state with results in agreement with BCS theory. An analysis of the (115)In nuclear quadrupole resonance spin-lattice relaxation rate T(1)(-1) measurements under pressure reveals the presence of 2d magnetic quantum critical fluctuations in the heavy-electron component that are a promising candidate for the pairing mechanism in this material. Our results are consistent with an antiferromagnetic quantum critical point located at slightly negative pressure in CeCoIn(5) and provide additional evidence for significant similarities between the heavy-electron materials and the high-T(c) cuprates.
Curro, N J
Nuclear magnetic resonance in the heavy fermion superconductors Journal Article
In: Rep. Prog. Phys., vol. 72, no. 2, pp. 026502 (24pp), 2009.
@article{Curro2009,
title = {Nuclear magnetic resonance in the heavy fermion superconductors},
author = {N J Curro},
url = {http://stacks.iop.org/0034-4885/72/026502},
doi = {10.1088/0034-4885/72/2/026502},
year = {2009},
date = {2009-01-01},
journal = {Rep. Prog. Phys.},
volume = {72},
number = {2},
pages = {026502 (24pp)},
abstract = {Nuclear magnetic resonance has emerged as a vital technique for investigating strongly correlated electron systems, and is particularly important for studying superconductivity. In this paper the basic features of NMR as a technique for probing the superconducting state are reviewed. Topics include spin relaxation processes, studies of vortex lattices and phenomena associated with unconventional pairing symmetries. Recent experimental work is reviewed, with a particular emphasis on the heavy fermion superconductors.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Nuclear magnetic resonance has emerged as a vital technique for investigating strongly correlated electron systems, and is particularly important for studying superconductivity. In this paper the basic features of NMR as a technique for probing the superconducting state are reviewed. Topics include spin relaxation processes, studies of vortex lattices and phenomena associated with unconventional pairing symmetries. Recent experimental work is reviewed, with a particular emphasis on the heavy fermion superconductors.
Curro, N. J.; Urbano, R. R.; Young, B. -L.
Probing the magnetism in the CeMIn$_5$ heavy fermion systems by NMR Journal Article
In: Phys. B, vol. 403, no. 5-9, pp. 1010–1012, 2008, ISSN: 0921-4526, (International Conference on Strongly Correlated Electron Systems (SCES 2007), Houston, TX, May 13-18, 2007).
@article{Curro2008,
title = {Probing the magnetism in the CeMIn$_5$ heavy fermion systems by NMR},
author = {N. J. Curro and R. R. Urbano and B. -L. Young},
doi = {10.1016/j.physb.2007.10.242},
issn = {0921-4526},
year = {2008},
date = {2008-04-01},
journal = {Phys. B},
volume = {403},
number = {5-9},
pages = {1010--1012},
organization = {Inst Complex Adapt Matter; Natl Sci Fdn; Brookhaven Natl Lab; Oak Ridge Natl Lab, Mat Sci & Technol Div; Oak Ridge Natl Lab, Spallat Neutron Source; Florida State Univ, Natl High Magnet Field Lab; Univ Houston, Texas Ctr Superconduct; Univ Houston, Div Res & Dept Phys; Rice Univ, Wiess Sch Nat Sci, Off Dean; Rice Univ, Dept Phys & Astron; Rice Univ, Vice Provost Res & Grad Studies},
abstract = {The CeMIn$_5$ heavy fermion system exhibits antiferromagnetism for both M = Rh and M = Co. CeRhIn$_5$ is antiferromagnetic at ambient pressure and superconducting under hydrostatic pressure, whereas CeCoIn$_5$ is superconducting at ambient pressure, but becomes antiferromagnetic with substitution of In by a few percent of Cd. Pure CeCoIn$_5$ exhibits a field-induced magnetic phase that coexists with the superconductivity. Nuclear magnetic resonance (NMR) and nuclear quadrupolar resonance (NQR) studies of the In(1), In(2) and Co sites reveal similar features in the magnetic states of these systems. (c) 2007 Published by Elsevier B.V.},
note = {International Conference on Strongly Correlated Electron Systems (SCES 2007), Houston, TX, May 13-18, 2007},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The CeMIn$_5$ heavy fermion system exhibits antiferromagnetism for both M = Rh and M = Co. CeRhIn$_5$ is antiferromagnetic at ambient pressure and superconducting under hydrostatic pressure, whereas CeCoIn$_5$ is superconducting at ambient pressure, but becomes antiferromagnetic with substitution of In by a few percent of Cd. Pure CeCoIn$_5$ exhibits a field-induced magnetic phase that coexists with the superconductivity. Nuclear magnetic resonance (NMR) and nuclear quadrupolar resonance (NQR) studies of the In(1), In(2) and Co sites reveal similar features in the magnetic states of these systems. (c) 2007 Published by Elsevier B.V.
Thompson, J. D.; Curro, N. J.; Park, Tuson; Bauer, E. D.; Sarrao, J. L.
PuCoGa$_5$ and related materials Journal Article
In: J. Alloys Compd., vol. 444, pp. 19–22, 2007, ISSN: 0925-8388, (4th Topical Conference on Plutonium and Actinides/Plutonium Futures - The Science 2006, Pacific Grove, CA, JUL 09-13, 2006).
@article{Thompson2007,
title = {PuCoGa$_5$ and related materials},
author = {J. D. Thompson and N. J. Curro and Tuson Park and E. D. Bauer and J. L. Sarrao},
doi = {10.1016/j.jallcom.2006.09.046},
issn = {0925-8388},
year = {2007},
date = {2007-10-01},
journal = {J. Alloys Compd.},
volume = {444},
pages = {19--22},
organization = {Lawrence Livermore Natl Lab; Los Alamos Natl Lab; Amer Nucl Soc; Quantum Design Co; FEI Co},
abstract = {Temperature dependencies of the nuclear spin-relaxation rate and specific heat of PuCoGa$_5$ and isostructural PuRbGa5 are consistent with their superconductivity being unconventional. A simple model of hybridization between localized f-electrons and itinerant conduction-band electrons gives a framework for interpreting basic similarities and differences between these Pu-based superconductors and their Ce-based analogs. This model also provides a rationale for the correlation between T, and a characteristic spin-energy scale in these materials. (c) 2006 Elsevier B.V. All rights reserved.},
note = {4th Topical Conference on Plutonium and Actinides/Plutonium Futures - The Science 2006, Pacific Grove, CA, JUL 09-13, 2006},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Temperature dependencies of the nuclear spin-relaxation rate and specific heat of PuCoGa$_5$ and isostructural PuRbGa5 are consistent with their superconductivity being unconventional. A simple model of hybridization between localized f-electrons and itinerant conduction-band electrons gives a framework for interpreting basic similarities and differences between these Pu-based superconductors and their Ce-based analogs. This model also provides a rationale for the correlation between T, and a characteristic spin-energy scale in these materials. (c) 2006 Elsevier B.V. All rights reserved.
Urbano, R. R.; Young, B. -L.; Curro, N. J.; Thompson, J. D.; Pham, L. D.; Fisk, Z.
Interacting antiferromagnetic droplets in quantum critical CeCoIn$_5$ Journal Article
In: Phys. Rev. Lett., vol. 99, no. 14, pp. 146402, 2007, ISSN: 0031-9007.
@article{Urbano2007,
title = {Interacting antiferromagnetic droplets in quantum critical CeCoIn$_5$},
author = {R. R. Urbano and B. -L. Young and N. J. Curro and J. D. Thompson and L. D. Pham and Z. Fisk},
doi = {10.1103/PhysRevLett.99.146402},
issn = {0031-9007},
year = {2007},
date = {2007-10-01},
journal = {Phys. Rev. Lett.},
volume = {99},
number = {14},
pages = {146402},
abstract = {The heavy fermion superconductor CeCoIn$_5$ can be tuned between superconducting and antiferromagnetic ground states by hole doping with Cd. Nuclear magnetic resonance data indicate that these two orders coexist microscopically with an ordered moment similar to 0.7 mu(B). As the ground state evolves, there is no change in the low-frequency spin dynamics in the disordered state. These results suggest that the magnetism emerges locally in the vicinity of the Cd dopants.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The heavy fermion superconductor CeCoIn$_5$ can be tuned between superconducting and antiferromagnetic ground states by hole doping with Cd. Nuclear magnetic resonance data indicate that these two orders coexist microscopically with an ordered moment similar to 0.7 mu(B). As the ground state evolves, there is no change in the low-frequency spin dynamics in the disordered state. These results suggest that the magnetism emerges locally in the vicinity of the Cd dopants.
Young, B. -L.; Urbano, R. R.; Curro, N. J.; Thompson, J. D.; Sarrao, J. L.; Vorontsov, A. B.; Graf, M. J.
Microscopic evidence for field-induced magnetism in CeCoIn$_5$ Journal Article
In: Phys. Rev. Lett., vol. 98, no. 3, pp. 036402, 2007, ISSN: 0031-9007.
@article{Young2007,
title = {Microscopic evidence for field-induced magnetism in CeCoIn$_5$},
author = {B. -L. Young and R. R. Urbano and N. J. Curro and J. D. Thompson and J. L. Sarrao and A. B. Vorontsov and M. J. Graf},
doi = {10.1103/PhysRevLett.98.036402},
issn = {0031-9007},
year = {2007},
date = {2007-01-01},
journal = {Phys. Rev. Lett.},
volume = {98},
number = {3},
pages = {036402},
abstract = {We present NMR data in the normal and superconducting states of CeCoIn$_5$ for fields close to H-c2(0)=11.8 T in the ab plane. Recent experiments identified a first-order transition from the normal to superconducting state for H > 10.5 T, and a new thermodynamic phase below 290 mK within the superconducting state. We find that the Knight shifts of the In(1), In(2), and the Co are discontinuous across the first-order transition and the magnetic linewidths increase dramatically. The broadening differs for the three sites, unlike the expectation for an Abrikosov vortex lattice, and suggests the presence of static spin moments in the vortex cores. In the low-temperature and high-field phase, the broad NMR lineshapes suggest ordered local moments, rather than a long-wavelength quasiparticle spin density modulation expected for an FFLO phase.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present NMR data in the normal and superconducting states of CeCoIn$_5$ for fields close to H-c2(0)=11.8 T in the ab plane. Recent experiments identified a first-order transition from the normal to superconducting state for H > 10.5 T, and a new thermodynamic phase below 290 mK within the superconducting state. We find that the Knight shifts of the In(1), In(2), and the Co are discontinuous across the first-order transition and the magnetic linewidths increase dramatically. The broadening differs for the three sites, unlike the expectation for an Abrikosov vortex lattice, and suggests the presence of static spin moments in the vortex cores. In the low-temperature and high-field phase, the broad NMR lineshapes suggest ordered local moments, rather than a long-wavelength quasiparticle spin density modulation expected for an FFLO phase.
Curro, N. J.
Hyperfine interactions in the heavy fermion CeMIn$_5$ systems Journal Article
In: New J. Phys., vol. 8, pp. 178, 2006, ISSN: 1367-2630.
@article{Curro2006a,
title = {Hyperfine interactions in the heavy fermion CeMIn$_5$ systems},
author = {N. J. Curro},
doi = {10.1088/1367-2630/8/9/173},
issn = {1367-2630},
year = {2006},
date = {2006-09-01},
journal = {New J. Phys.},
volume = {8},
pages = {178},
abstract = {The CeMIn$_5$ heavy fermion compounds have attracted enormous interest since their discovery six years ago. These materials exhibit a rich spectrum of unusual correlated electron behaviour, and may be an ideal model for the high-temperature superconductors. As many of these systems are either antiferromagnets, or lie close to an antiferromagnetic phase boundary, it is crucial to understand the behaviour of the dynamic and static magnetism. Since neutron scattering is difficult in these materials, often the primary source of information about the magnetic fluctuations is nuclear magnetic resonance. Therefore, it is crucial to have a detailed understanding of how the nuclear moments interact with conduction electrons and the local moments present in these systems. Here, we present a detailed analysis of the hyperfine coupling based on anisotropic hyperfine coupling tensors between nuclear moments and local moments. Because the couplings are symmetric with respect to bond axes rather than crystal lattice directions, the nuclear sites can experience non-vanishing hyperfine fields even in high symmetry sites.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The CeMIn$_5$ heavy fermion compounds have attracted enormous interest since their discovery six years ago. These materials exhibit a rich spectrum of unusual correlated electron behaviour, and may be an ideal model for the high-temperature superconductors. As many of these systems are either antiferromagnets, or lie close to an antiferromagnetic phase boundary, it is crucial to understand the behaviour of the dynamic and static magnetism. Since neutron scattering is difficult in these materials, often the primary source of information about the magnetic fluctuations is nuclear magnetic resonance. Therefore, it is crucial to have a detailed understanding of how the nuclear moments interact with conduction electrons and the local moments present in these systems. Here, we present a detailed analysis of the hyperfine coupling based on anisotropic hyperfine coupling tensors between nuclear moments and local moments. Because the couplings are symmetric with respect to bond axes rather than crystal lattice directions, the nuclear sites can experience non-vanishing hyperfine fields even in high symmetry sites.
Curro, NJ; Caldwell, T; Bauer, ED; Morales, LA; Graf, M; Bang, Y; Balatsky, A; Thompson, JD; Sarrao, JL
Unconventional superconductivity in PuCoGa$_5$ Journal Article
In: Phys. B, vol. 378-80, pp. 915–919, 2006, ISSN: 0921-4526, (International Conference on Strongly Correlated Electron Systems (SECES 05), Vienna, Austria, Jul 26-30, 2005).
@article{Curro2006,
title = {Unconventional superconductivity in PuCoGa$_5$},
author = {NJ Curro and T Caldwell and ED Bauer and LA Morales and M Graf and Y Bang and A Balatsky and JD Thompson and JL Sarrao},
doi = {10.1016/j.physb.2006.01.352},
issn = {0921-4526},
year = {2006},
date = {2006-05-01},
journal = {Phys. B},
volume = {378-80},
pages = {915--919},
abstract = {We report nuclear magnetic resonance (NMR) data in the new heavy fermion Superconductor PuCoGa$_5$ (T-c = 18.5 K) in the normal and superconducting states. Measurements of the Knight shift and the nuclear spin lattice relaxation rate in the superconducting state show a spin-singlet with lines of nodes in the gap function, and our calculations indicate that the data are consistent with a strong-coupling d-wave gap function with Delta/k(B)T(c) = 4. In the normal state. the temperature dependence of the spin lattice relaxation rate suggests the presence of antiferromagnetic correlations, and scales with T, in the same manner as in other heavy fermion superconductors, as well as the high-temperature superconductor. YBa2Cu3O7. Published by Elsevier B.V.},
note = {International Conference on Strongly Correlated Electron Systems (SECES 05), Vienna, Austria, Jul 26-30, 2005},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report nuclear magnetic resonance (NMR) data in the new heavy fermion Superconductor PuCoGa$_5$ (T-c = 18.5 K) in the normal and superconducting states. Measurements of the Knight shift and the nuclear spin lattice relaxation rate in the superconducting state show a spin-singlet with lines of nodes in the gap function, and our calculations indicate that the data are consistent with a strong-coupling d-wave gap function with Delta/k(B)T(c) = 4. In the normal state. the temperature dependence of the spin lattice relaxation rate suggests the presence of antiferromagnetic correlations, and scales with T, in the same manner as in other heavy fermion superconductors, as well as the high-temperature superconductor. YBa2Cu3O7. Published by Elsevier B.V.
Thompson, J. D.; Park, Tuson; Curro, N. J.; Sarrao, J. L.
Progress and Puzzles in Plutonium Superconductors Journal Article
In: J. Phys. Soc. Jpn., vol. 75S, pp. 1–3, 2006.
@article{Thompson2006a,
title = {Progress and Puzzles in Plutonium Superconductors},
author = {J. D. Thompson and Tuson Park and N. J. Curro and J. L. Sarrao},
url = {http://jpsj.ipap.jp/link?JPSJS/75S/1/},
doi = {10.1143/JPSJS.75S.1},
year = {2006},
date = {2006-01-01},
journal = {J. Phys. Soc. Jpn.},
volume = {75S},
pages = {1--3},
publisher = {The Physical Society of Japan},
abstract = {Recent progress revealing the unconventional nature of both normal and superconducting states of PuCoGa$_5$ and PuRhGa5 has cast these materials in a broader context of strongly correlated materials and phenomena. In this regard, a comparison of the Pu-based superconductors to their isostructural Ce-based counterparts suggests a set of experiments that might lead to a clearer definition of the puzzles they present.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recent progress revealing the unconventional nature of both normal and superconducting states of PuCoGa$_5$ and PuRhGa5 has cast these materials in a broader context of strongly correlated materials and phenomena. In this regard, a comparison of the Pu-based superconductors to their isostructural Ce-based counterparts suggests a set of experiments that might lead to a clearer definition of the puzzles they present.
Curro, N.; Fisk, Z.; Pines, D.
Scaling and the magnetic origin of emergent behavior in correlated electron superconductors Journal Article
In: MRS Bull., vol. 30, no. 6, pp. 442–446, 2005.
@article{Curro2005a,
title = {Scaling and the magnetic origin of emergent behavior in correlated electron superconductors},
author = {N. Curro and Z. Fisk and D. Pines},
doi = {http://dx.doi.org/10.1557/mrs2005.121},
year = {2005},
date = {2005-06-01},
journal = {MRS Bull.},
volume = {30},
number = {6},
pages = {442--446},
abstract = {We discuss three examples of emergent behavior in correlated electron matter, in which the discovery of scaling of several measured quantities with a single energy scale provides a key clue to a common magnetic origin: the emergence of itinerant (mobile) electronic behavior from the Kondo lattice of localized f electrons found in cerium- and uranium-based heavy fermion materials; the emergence of unconventional superconductivity in the cuprate and “high-temperature” heavy electron Ce- and Pu-based 1-1-5 superconductors; and the emergence of pseudogap behavior in the underdoped and optimally doped cuprate superconductors.We conclude with some speculation on ways in which these novel perspectives might be used to design new materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We discuss three examples of emergent behavior in correlated electron matter, in which the discovery of scaling of several measured quantities with a single energy scale provides a key clue to a common magnetic origin: the emergence of itinerant (mobile) electronic behavior from the Kondo lattice of localized f electrons found in cerium- and uranium-based heavy fermion materials; the emergence of unconventional superconductivity in the cuprate and “high-temperature” heavy electron Ce- and Pu-based 1-1-5 superconductors; and the emergence of pseudogap behavior in the underdoped and optimally doped cuprate superconductors.We conclude with some speculation on ways in which these novel perspectives might be used to design new materials.
Young, BL; Curro, NJ; Sidorov, VA; Thompson, JD; Sarrao, JL
NQR and $T_1$ studies of the high-pressure phase in YbInCu$_4$ Journal Article
In: Phys. Rev. B, vol. 71, no. 22, pp. 224106, 2005, ISSN: 1098-0121.
@article{Young2005,
title = {NQR and $T_1$ studies of the high-pressure phase in YbInCu$_4$},
author = {BL Young and NJ Curro and VA Sidorov and JD Thompson and JL Sarrao},
doi = {10.1103/PhysRevB.71.224106},
issn = {1098-0121},
year = {2005},
date = {2005-06-01},
journal = {Phys. Rev. B},
volume = {71},
number = {22},
pages = {224106},
abstract = {The pressure and temperature phase diagram of YbInCu4 has been investigated by nuclear quadrupolar resonance (NQR) and spin-lattice relaxation rate (T-1(-1)) experiments. The pressure dependence of the Cu-63 NQR frequency indicates that the first-order valence transition temperature, T-v, does not vanish continuously at the critical pressure (P(c)approximate to 23.7 kbar) and thus there is no quantum critical point (T-v=0) in YbInCu4. This result is consistent with the T-1(-1) data, which show no evidence for non-Fermi-liquid behavior near P-c. For pressures P greater than or similar to P-c, T-1(-1) increases sharply near 2.4 K, which suggests the presence of critical fluctuations associated with ferromagnetic (FM) ordering. We analyze the T-1(-1), resistivity, and the pressure-enhanced susceptibility data in the mixed-valent state of YbInCu4 and find no evidence to indicate that the pressure-induced FM phase can be described by the Stoner theory for itinerant ferromagnetism. Rather, the pressure-induced FM order may be due to pressure-stabilized Yb3+ local moments. We also examine the possibility of FM order induced by an external magnetic field near P-c, but find no evidence down to 1.5 K.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The pressure and temperature phase diagram of YbInCu4 has been investigated by nuclear quadrupolar resonance (NQR) and spin-lattice relaxation rate (T-1(-1)) experiments. The pressure dependence of the Cu-63 NQR frequency indicates that the first-order valence transition temperature, T-v, does not vanish continuously at the critical pressure (P(c)approximate to 23.7 kbar) and thus there is no quantum critical point (T-v=0) in YbInCu4. This result is consistent with the T-1(-1) data, which show no evidence for non-Fermi-liquid behavior near P-c. For pressures P greater than or similar to P-c, T-1(-1) increases sharply near 2.4 K, which suggests the presence of critical fluctuations associated with ferromagnetic (FM) ordering. We analyze the T-1(-1), resistivity, and the pressure-enhanced susceptibility data in the mixed-valent state of YbInCu4 and find no evidence to indicate that the pressure-induced FM phase can be described by the Stoner theory for itinerant ferromagnetism. Rather, the pressure-induced FM order may be due to pressure-stabilized Yb3+ local moments. We also examine the possibility of FM order induced by an external magnetic field near P-c, but find no evidence down to 1.5 K.
Curro, NJ; Caldwell, T; Bauer, ED; Morales, LA; Graf, MJ; Bang, Y; Balatsky, AV; Thompson, JD; Sarrao, JL
Unconventional superconductivity in PuCoGa$_5$ Journal Article
In: Nature, vol. 434, no. 7033, pp. 622–625, 2005, ISSN: 0028-0836.
@article{Curro2005,
title = {Unconventional superconductivity in PuCoGa$_5$},
author = {NJ Curro and T Caldwell and ED Bauer and LA Morales and MJ Graf and Y Bang and AV Balatsky and JD Thompson and JL Sarrao},
doi = {10.1038/nature03428},
issn = {0028-0836},
year = {2005},
date = {2005-03-01},
journal = {Nature},
volume = {434},
number = {7033},
pages = {622--625},
abstract = {In the Bardeen-Cooper-Schrieffer theory of superconductivity, electrons form ( Cooper) pairs through an interaction mediated by vibrations in the underlying crystal structure. Like lattice vibrations, antiferromagnetic fluctuations can also produce an attractive interaction creating Cooper pairs, though with spin and angular momentum properties different from those of conventional superconductors. Such interactions have been implicated for two disparate classes of materials-the copper oxides(1,2) and a set of Ce- and U-based compounds(3). But because their transition temperatures differ by nearly two orders of magnitude, this raises the question of whether a common pairing mechanism applies. PuCoGa$_5$ has a transition temperature intermediate between those classes and therefore may bridge these extremes(4). Here we report measurements of the nuclear spin-lattice relaxation rate and Knight shift in PuCoGa$_5$, which demonstrate that it is an unconventional superconductor with properties as expected for antiferromagnetically mediated superconductivity. Scaling of the relaxation rates among all of these materials ( a feature not exhibited by their Knight shifts) establishes antiferromagnetic fluctuations as a likely mechanism for their unconventional superconductivity and suggests that related classes of exotic superconductors may yet be discovered.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In the Bardeen-Cooper-Schrieffer theory of superconductivity, electrons form ( Cooper) pairs through an interaction mediated by vibrations in the underlying crystal structure. Like lattice vibrations, antiferromagnetic fluctuations can also produce an attractive interaction creating Cooper pairs, though with spin and angular momentum properties different from those of conventional superconductors. Such interactions have been implicated for two disparate classes of materials-the copper oxides(1,2) and a set of Ce- and U-based compounds(3). But because their transition temperatures differ by nearly two orders of magnitude, this raises the question of whether a common pairing mechanism applies. PuCoGa$_5$ has a transition temperature intermediate between those classes and therefore may bridge these extremes(4). Here we report measurements of the nuclear spin-lattice relaxation rate and Knight shift in PuCoGa$_5$, which demonstrate that it is an unconventional superconductor with properties as expected for antiferromagnetically mediated superconductivity. Scaling of the relaxation rates among all of these materials ( a feature not exhibited by their Knight shifts) establishes antiferromagnetic fluctuations as a likely mechanism for their unconventional superconductivity and suggests that related classes of exotic superconductors may yet be discovered.