Heavy Fermion Superconductivity
We studied the unusual superconductivity in various heavy fermion superconductors. The prototypical heavy fermion superconductor is CeCoIn5, which has a transition temperature of 2.3 K. Although this is not a very high temperature, this system enables us to investigate a wealth of behaviors that would not be possible with other superconductors with higher transition temperatures.
The superconducting state of CeCoIn5 is unusual because this material lies close to the boundary of antiferromagnetism. The electrons would like to order their spins, but if they do so there is a cost to pay in terms of the superconducting condensation energy. On the other hand, if they form a superconducting condensate with singlet pairing, they are unable to reduce their magnetic energy as when they align antiferromagnetically. For a small region of phase space, the system exhibits a novel type of order in which both antiferromagnetism and superconductivity coexist, now known as the Q phase. Our NMR work was the first to identify the presence of antiferromagnetism in this state.
We researched the behavior of superconductivity and antiferromagnetism in the presence of disorder. When Cd is substituted into CeCoIn5, it nucleates islands of antiferromagnetism. These islands coexist with the superconductivity inhomogeneously, until the islands grow so large they completely suppress the superconductivity.
We identified the presence of d-wave superconductivity in PuCoGa5, which has the highest Tc for a heavy fermion material at 17.5 K. This work was instrumental in understanding how the heavy fermion superconductors, with small Tc‘s, could be connected with the high Tc superconductors, with Tc‘s over 100 K, simply by tuning the size of the magnetic coupling.
Relevant Publications
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}
}
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}
}
Shirer, K. R.; Lawson, M.; Kissikov, T.; Bush, B. T.; Gallagher, A.; Chen, K. -W.; Baumbach, R. E.; Curro, N. J.
NMR investigation of antiferromagnetism and coherence in URu$_2$Si$_2-x$P$_x$ Journal Article
In: Phys. Rev. B, vol. 95, pp. 041107, 2017.
@article{ShirerPdopedURS2017,
title = {NMR investigation of antiferromagnetism and coherence in URu$_2$Si$_2-x$P$_x$},
author = {K. R. Shirer and M. Lawson and T. Kissikov and B. T. Bush and A. Gallagher and K. -W. Chen and R. E. Baumbach and N. J. Curro},
url = {http://link.aps.org/doi/10.1103/PhysRevB.95.041107},
doi = {10.1103/PhysRevB.95.041107},
year = {2017},
date = {2017-01-01},
journal = {Phys. Rev. B},
volume = {95},
pages = {041107},
publisher = {American Physical Society},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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 = {},
pubstate = {published},
tppubtype = {article}
}
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},
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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.
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},
tppubtype = {article}
}
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. D.; apRoberts-Warren, N.; Klavins, P.; Curro, N. J.
Probing Onset of Coherence in CeIrIn$_5$ Journal Article
In: J. Phys: Conf. Ser., vol. 344, pp. 012020, 2012.
@article{Shockley2011,
title = {Probing Onset of Coherence in CeIrIn$_5$},
author = {A. C. Shockley and A. D. Dioguardi and N. apRoberts-Warren and P. Klavins and N. J. Curro},
doi = {10.1088/1742-6596/344/1/012020},
year = {2012},
date = {2012-01-01},
journal = {J. Phys: Conf. Ser.},
volume = {344},
pages = {012020},
abstract = {We report 115In NMR measurements in the heavy fermion superconductor CeIrIn$_5$. The Knight shift for the symmetric In(1) site displays the same behaviour as the related material CeCoIn$_5$. Our results support the phenomenological two-fluid model proposed by Nakatsuji et al. Comparison to recent DMFT calculations for CeIrIn$_5$ further strengthens our conclusions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report 115In NMR measurements in the heavy fermion superconductor CeIrIn$_5$. The Knight shift for the symmetric In(1) site displays the same behaviour as the related material CeCoIn$_5$. Our results support the phenomenological two-fluid model proposed by Nakatsuji et al. Comparison to recent DMFT calculations for CeIrIn$_5$ further strengthens our conclusions.
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.
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.},
keywords = {},
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tppubtype = {article}
}
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.
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},
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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.
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.
Spehling, J.; Heffner, R. H.; Sonier, J. E.; Curro, N.; Wang, C. H.; Hitti, B.; Morris, G.; Bauer, E. D.; Sarrao, J. L.; Litterst, F. J.; Klauss, H. -H.
Field-Induced Coupled Superconductivity and Spin Density Wave Order in the Heavy Fermion Compound CeCoIn$_5$ Journal Article
In: Phys. Rev. Lett., vol. 103, pp. 237003, 2009.
@article{Spehling2009,
title = {Field-Induced Coupled Superconductivity and Spin Density Wave Order in the Heavy Fermion Compound CeCoIn$_5$},
author = {J. Spehling and R. H. Heffner and J. E. Sonier and N. Curro and C. H. Wang and B. Hitti and G. Morris and E. D. Bauer and J. L. Sarrao and F. J. Litterst and H. -H. Klauss},
doi = {10.1103/PhysRevLett.103.237003},
year = {2009},
date = {2009-12-01},
journal = {Phys. Rev. Lett.},
volume = {103},
pages = {237003},
publisher = {American Physical Society},
abstract = {The high field superconducting state in CeCoIn$_5$ has been studied by transverse field muon spin rotation measurements with an applied field parallel to the crystallographic c-axis close to the upper critical field Hc2 = 4.97 T. At magnetic fields 4.8 T the muon Knight shift is enhanced and the superconducting transition changes from second order towards first order as predicted for Pauli-limited superconductors. The field and temperature dependence of the transverse muon spin relaxation rate sigma reveal paramagnetic spin fluctuations in the field regime from 2 T < H < 4.8 T. In the normal state close to Hc2 correlated spin fluctuations as described by the self consistent renormalization theory are observed. The results support the formation of a mode-coupled superconducting and antiferromagnetically ordered phase in CeCoIn$_5$ for H directed parallel to the c-axis.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The high field superconducting state in CeCoIn$_5$ has been studied by transverse field muon spin rotation measurements with an applied field parallel to the crystallographic c-axis close to the upper critical field Hc2 = 4.97 T. At magnetic fields 4.8 T the muon Knight shift is enhanced and the superconducting transition changes from second order towards first order as predicted for Pauli-limited superconductors. The field and temperature dependence of the transverse muon spin relaxation rate sigma reveal paramagnetic spin fluctuations in the field regime from 2 T < H < 4.8 T. In the normal state close to Hc2 correlated spin fluctuations as described by the self consistent renormalization theory are observed. The results support the formation of a mode-coupled superconducting and antiferromagnetically ordered phase in CeCoIn$_5$ for H directed parallel to the c-axis.
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.; Pines, D.
Anisotropic spin fluctuations in CeCoIn$_5$ Journal Article
In: J. Phys. Chem. Solids, vol. 68, no. 11, SI, pp. 2028–2030, 2007, ISSN: 0022-3697, (1st International Symposium of Quantum Beam Science Directorate, Tokai, Japan, Aug 20-25, 2006).
@article{Curro2007,
title = {Anisotropic spin fluctuations in CeCoIn$_5$},
author = {N. J. Curro and D. Pines},
doi = {10.1016/j.jpcs.2007.08.020},
issn = {0022-3697},
year = {2007},
date = {2007-11-01},
journal = {J. Phys. Chem. Solids},
volume = {68},
number = {11, SI},
pages = {2028--2030},
organization = {Japan Atom Energy Agcy},
abstract = {CeCoIn$_5$ is an unconventional heavy fermion superconductor with a relatively large transition temperature T-c = 2.3 K. NMR measurements of the spin lattice relaxation rate at the In(1) site reveal a significant anisotropy of the fluctuating hyperfine fields, which reverses below 30 K. These results suggest that two-dimensional fluctuations of the Ce 4f moments are relevant for the superconducting pairing. Published by Elsevier Ltd.},
note = {1st International Symposium of Quantum Beam Science Directorate, Tokai, Japan, Aug 20-25, 2006},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
CeCoIn$_5$ is an unconventional heavy fermion superconductor with a relatively large transition temperature T-c = 2.3 K. NMR measurements of the spin lattice relaxation rate at the In(1) site reveal a significant anisotropy of the fluctuating hyperfine fields, which reverses below 30 K. These results suggest that two-dimensional fluctuations of the Ce 4f moments are relevant for the superconducting pairing. Published by Elsevier Ltd.
Bang, Yunkyu; Graf, M. J.; Curro, N. J.; Balatsky, A. V.
The nuclear spin-lattice relaxation rate in the PuMGa$_5$ materials Journal Article
In: J. Magn. Magn. Mater., vol. 310, no. 2, Part 1, pp. 634–636, 2007, ISSN: 0304-8853, (17th International Conference on Magnetism (ICM 2006), Kyoto, Japan, AUG 20-25, 2006).
@article{Bang2007,
title = {The nuclear spin-lattice relaxation rate in the PuMGa$_5$ materials},
author = {Yunkyu Bang and M. J. Graf and N. J. Curro and A. V. Balatsky},
doi = {10.1016/j.jmmm.2006.10.277},
issn = {0304-8853},
year = {2007},
date = {2007-03-01},
journal = {J. Magn. Magn. Mater.},
volume = {310},
number = {2, Part 1},
pages = {634--636},
organization = {Int Union Pure & Appl Phys},
abstract = {We examine the nuclear spin-lattice relaxation rates 1/T-1 of PuRhGa5 and PuCoGa$_5$, in particular, in normal state. PuRhGa5 exhibits a gradual suppression of (T1T)(-1) below 25K far above T-c similar to 8.5K, while measurements for PuCoGa$_5$ reveal a monotonic increase down to T-c. We propose that this behavior is consistently understood by the crossover from the two-dimensional quantum antiferromagnetic regime of the local 5f-electron spins of Pu to the concomitant formation of the fermion pseudogap based on the two-component spin-fermion model. (c) 2006 Elsevier B.V. All rights reserved.},
note = {17th International Conference on Magnetism (ICM 2006), Kyoto, Japan, AUG 20-25, 2006},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We examine the nuclear spin-lattice relaxation rates 1/T-1 of PuRhGa5 and PuCoGa$_5$, in particular, in normal state. PuRhGa5 exhibits a gradual suppression of (T1T)(-1) below 25K far above T-c similar to 8.5K, while measurements for PuCoGa$_5$ reveal a monotonic increase down to T-c. We propose that this behavior is consistently understood by the crossover from the two-dimensional quantum antiferromagnetic regime of the local 5f-electron spins of Pu to the concomitant formation of the fermion pseudogap based on the two-component spin-fermion model. (c) 2006 Elsevier B.V. All rights reserved.
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.
Bang, Yunkyu; Graf, M. J.; Curro, N. J.; Balatsky, A. V.
Nuclear spin-lattice relaxation rate in PuMGa$_5$ (M=Rh, Co): A two-component spin-fermion model Journal Article
In: Phys. Rev. B, vol. 74, no. 5, pp. 054514, 2006, ISSN: 1098-0121.
@article{Bang2006,
title = {Nuclear spin-lattice relaxation rate in PuMGa$_5$ (M=Rh, Co): A two-component spin-fermion model},
author = {Yunkyu Bang and M. J. Graf and N. J. Curro and A. V. Balatsky},
doi = {10.1103/PhysRevB.74.054514},
issn = {1098-0121},
year = {2006},
date = {2006-08-01},
journal = {Phys. Rev. B},
volume = {74},
number = {5},
pages = {054514},
abstract = {We examine the nuclear spin-lattice relaxation rates 1/T-1 of PuRhGa5 and PuCoGa$_5$, both in the superconducting and normal states, as well as their Knight shifts. Results for both compounds are consistent with a superconducting gap of d-wave symmetry in the presence of strong impurity scattering, though with quite different gap-over-T-c ratios 2 Delta(0)/k(B)T(c) (eight for PuCoGa$_5$ and five for PuRhGa5). In the normal state, PuRhGa5 exhibits a gradual suppression of (T1T)(-1) below 25 K, while measurements for PuCoGa$_5$ reveal a monotonic increase down to T-c. We propose that this behavior is consistently understood by the crossover of the two-dimensional quantum antiferromagnetic correlation of the local 5f-electron spins of Pu and the concomitant formation of the fermion pseudogap based on the two-component spin-fermion model.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We examine the nuclear spin-lattice relaxation rates 1/T-1 of PuRhGa5 and PuCoGa$_5$, both in the superconducting and normal states, as well as their Knight shifts. Results for both compounds are consistent with a superconducting gap of d-wave symmetry in the presence of strong impurity scattering, though with quite different gap-over-T-c ratios 2 Delta(0)/k(B)T(c) (eight for PuCoGa$_5$ and five for PuRhGa5). In the normal state, PuRhGa5 exhibits a gradual suppression of (T1T)(-1) below 25 K, while measurements for PuCoGa$_5$ reveal a monotonic increase down to T-c. We propose that this behavior is consistently understood by the crossover of the two-dimensional quantum antiferromagnetic correlation of the local 5f-electron spins of Pu and the concomitant formation of the fermion pseudogap based on the two-component spin-fermion model.
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.
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.
Bang, Yunkyu; Graf, Matthias J.; Curro, Nicholas J.; Balatsky, Alexander J.
Theory of the Knight Shift and Spin-Lattice Relaxation Rate in Pu-115 Journal Article
In: Materials Research Society Symposium - Proceedings, vol. 893, pp. 143–148, 2005.
@article{Bang2005,
title = {Theory of the Knight Shift and Spin-Lattice Relaxation Rate in Pu-115},
author = {Yunkyu Bang and Matthias J. Graf and Nicholas J. Curro and Alexander J. Balatsky},
doi = {http://dx.doi.org/10.1557/PROC-0893-JJ02-04},
year = {2005},
date = {2005-01-01},
journal = {Materials Research Society Symposium - Proceedings},
volume = {893},
pages = {143--148},
abstract = {We calculated the Knight shift and spin-lattice relaxation rates of Pu-115 compounds assuming d-wave superconductivity in the presence of strong impurity scattering. We discuss the implications for recent measurements of the spin-lattice relaxation rate in the Pu-115 compound PuRhGa5 by Sakai and coworkers [J. Phys. Soc. Jpn. 74, 1710 (2005)] and present a prediction for the corresponding Knight shift. In addition, we noticed a significant round-off of the spin-lattice relaxation rate 1/T1 just above the superconducting transition temperature that is not observed in the sister compound PuCoGa$_5$. It appears that in PuRhGa5 superconductivity is mediated by spin fluctuations, too. This provides additional support to the scenario of superconducting pairing mediated by spin fluctuations in the Pu-115 compounds similar to the Ce-115 compounds and the high-temperature copper-oxide superconductors.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We calculated the Knight shift and spin-lattice relaxation rates of Pu-115 compounds assuming d-wave superconductivity in the presence of strong impurity scattering. We discuss the implications for recent measurements of the spin-lattice relaxation rate in the Pu-115 compound PuRhGa5 by Sakai and coworkers [J. Phys. Soc. Jpn. 74, 1710 (2005)] and present a prediction for the corresponding Knight shift. In addition, we noticed a significant round-off of the spin-lattice relaxation rate 1/T1 just above the superconducting transition temperature that is not observed in the sister compound PuCoGa$_5$. It appears that in PuRhGa5 superconductivity is mediated by spin fluctuations, too. This provides additional support to the scenario of superconducting pairing mediated by spin fluctuations in the Pu-115 compounds similar to the Ce-115 compounds and the high-temperature copper-oxide superconductors.
Curro, NJ; Simovic, B; Hammel, PC; Pagliuso, PG; Sarrao, JL; Thompson, JD; Martins, GB
Anomalous NMR magnetic shifts in CeCoIn$_5$ Journal Article
In: Phys. Rev. B, vol. 64, no. 18, pp. 180514, 2001, ISSN: 0163-1829.
@article{Curro2001,
title = {Anomalous NMR magnetic shifts in CeCoIn$_5$},
author = {NJ Curro and B Simovic and PC Hammel and PG Pagliuso and JL Sarrao and JD Thompson and GB Martins},
doi = {10.1103/PhysRevB.64.180514},
issn = {0163-1829},
year = {2001},
date = {2001-11-01},
journal = {Phys. Rev. B},
volume = {64},
number = {18},
pages = {180514},
abstract = {We report In-115 and Co-59 nuclear magnetic resonance (NMR) measurements in the heavy fermion superconductor CeCoIn$_5$ above and below T-c. The hyperfine couplings of the In-115 and Co-59 are anisotropic and exhibit dramatic changes below 50 K due to changes in the crystal field level populations of the Ce ions. suggesting localized f electrons. Below T-c the spin susceptibility is suppressed, indicating singlet pairing.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report In-115 and Co-59 nuclear magnetic resonance (NMR) measurements in the heavy fermion superconductor CeCoIn$_5$ above and below T-c. The hyperfine couplings of the In-115 and Co-59 are anisotropic and exhibit dramatic changes below 50 K due to changes in the crystal field level populations of the Ce ions. suggesting localized f electrons. Below T-c the spin susceptibility is suppressed, indicating singlet pairing.