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Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd3 to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature-the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.

The transverse voltage generated by a temperature gradient in a perpendicularly applied magnetic field, termed the Nernst effect, has promise for thermoelectric applications and for probing electronic structure. In magnetic materials, an anomalous Nernst effect (ANE) is possible in a zero magnetic field. We report a colossal ANE in the ferromagnetic metal UCo0.8Ru0.2Al, reaching 23 microvolts per kelvin. Uranium's 5f electrons provide strong electronic correlations that lead to narrow bands, a known route to producing a large thermoelectric response. In addition, uranium's strong spin-orbit coupling produces an intrinsic transverse response in this material due to the Berry curvature associated with the relativistic electronic structure. Theoretical calculations show that in UCo0.8Ru0.2Al at least 148 Weyl nodes, and two nodal lines, exist within 60 millielectron volt of the Fermi level. This work demonstrates that magnetic actinide materials can host strong Nernst and Hall responses due to their combined correlated and topological nature.

Applied pressure drives the heavy-fermion antiferromagnet CeRhIn5 toward a quantum critical point that becomes hidden by a dome of unconventional superconductivity. Magnetic fields suppress this superconducting dome, unveiling the quantum phase transition of local character. Here, we show that [Formula: see text] magnetic substitution at the Ce site in CeRhIn5, either by Nd or Gd, induces a zero-field magnetic instability inside the superconducting state. This magnetic state not only should have a different ordering vector than the high-field local-moment magnetic state, but it also competes with the latter, suggesting that a spin-density-wave phase is stabilized in zero field by Nd and Gd impurities, similarly to the case of Ce0.95Nd0.05CoIn5 Supported by model calculations, we attribute this spin-density wave instability to a magnetic-impurity-driven condensation of the spin excitons that form inside the unconventional superconducting state.

SmB6 is a Kondo insulator with a band structure that is topologically distinct from the vacuum. This is theoretically predicted to produce metallic topological surface states that are robust to perturbations that do not break time reversal symmetry, such as non-magnetic defects. However, the surface state may be destroyed by an impurity with a sufficiently large magnetic moment. In order to test this prediction we show measurements of the resistance of the surface state of single crystals of SmB6 with varying levels of damage induced by magnetic and non-magnetic ion irradiation. We find that at a sufficiently high concentration of damage the surface state reconstructs below an amorphous damaged layer, whether the damage was caused by a magnetic or non-magnetic ion.

© 2015 Elsevier B.V. SmB6 is a Kondo insulator with a band structure that is topologically distinct from the vacuum. This is theoretically predicted to produce metallic topological surface states that are robust to perturbations that do not break time reversal symmetry, such as non-magnetic defects. However, the surface state may be destroyed by an impurity with a sufficiently large magnetic moment. In order to test this prediction we show measurements of the resistance of the surface state of single crystals of SmB6 with varying levels of damage induced by magnetic and non-magnetic ion irradiation. We find that at a sufficiently high concentration of damage the surface state reconstructs below an amorphous damaged layer, whether the damage was caused by a magnetic or non-magnetic ion.

We investigated the electrical resistivity and heat capacity of 1% Cd-doped CeIrIn_{5} under hydrostatic pressure up to 2.7 GPa, near where long-range antiferromagnetic order is suppressed and bulk superconductivity suddenly reemerges. The pressure-induced T_{c} is close to that of pristine CeIrIn_{5} at 2.7 GPa, and no signatures of a quantum critical point under pressure support a local origin of the antiferromagnetic moments in Cd-CeIrIn_{5} at ambient pressure. Similarities between superconductors CeIrIn_{5} and CeCoIn_{5} in response to Cd substitutions suggest a common magnetic mechanism.

We have used ion irradiation to damage the (001) surfaces of SmB6 single crystals to varying depths, and have measured the resistivity as a function of temperature for each depth of damage. We observe a reduction in the residual resistivity with increasing depth of damage. Our data are consistent with a model in which the surface state is not destroyed by the ion irradiation, but instead the damaged layer is poorly conducting and the initial surface state is reconstructed below the damage. This behavior is consistent with a surface state that is topologically protected.

Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to study the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ⩽ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ∼ T(3/2) and γ(T) ∼ γ0 - bT(1/2)). However, for 2 ⩽ T ⩽ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. Furthermore, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. We suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

We report a molten metal flux technique to produce high purity specimens of URu(Formula presented.)Si(Formula presented.). Magnetic susceptibility (Formula presented.)(Formula presented.)(Formula presented.), heat capacity (Formula presented.) and electrical resistivity (Formula presented.) measurements show that the bulk properties of these crystals are similar to those that are produced by the Czochralski technique followed by solid-state electro-transport. In particular, we find residual resistivity ratios RRR (Formula presented.)(Formula presented.)/(Formula presented.) as large as 220. © 2014 © 2014 Taylor & Francis.

We report a globally reversible effect of electronic tuning on the magnetic phase diagram in CeCoIn(5) driven by electron (Pt and Sn) and hole (Cd, Hg) doping. Consequently, we are able to extract the superconducting pair breaking component for hole and electron dopants with pressure and codoping studies, respectively. We find that these nominally nonmagnetic dopants have a remarkably weak pair breaking effect for a d-wave superconductor. The pair breaking is weaker for hole dopants, which induce magnetic moments, than for electron dopants. Furthermore, both Pt and Sn doping have a similar effect on superconductivity despite being on different dopant sites, arguing against the notion that superconductivity lives predominantly in the CeIn(3) planes of these materials. In addition, we shed qualitative understanding on the doping dependence with density functional theory calculations.

A current of electrons traversing a landscape of localized spins possessing non-coplanar magnetic order gains a geometrical (Berry) phase, which can lead to a Hall voltage independent of the spin-orbit coupling within the material-a geometrical Hall effect. Here we show that the highly correlated metal UCu(5) possesses an unusually large controllable geometrical Hall effect at T

Inhomogeneous electronic states resulting from entangled spin, charge, and lattice degrees of freedom are hallmarks of strongly correlated electron materials; such behavior has been observed in many classes of d-electron materials, including the high-Tc copper-oxide superconductors, manganites, and most recently the iron-pnictide superconductors. The complexity generated by competing phases in these materials constitutes a considerable theoretical challenge - one that still defies a complete description. Here, we report a manifestation of electronic inhomogeneity in a strongly correlated f-electron system, using CeCoIn5 as an example. A thermodynamic analysis of its superconductivity, combined with nuclear quadrupole resonance measurements, shows that nonmagnetic impurities (Y, La, Yb, Th, Hg, and Sn) locally suppress unconventional superconductivity, generating an inhomogeneous electronic "Swiss cheese" due to disrupted periodicity of the Kondo lattice. Our analysis may be generalized to include related systems, suggesting that electronic inhomogeneity should be considered broadly in Kondo lattice materials.

β-UB2C exhibits itinerant ferromagnetism below T c 75 K; whereas, UNiSi2 exhibits ferromagnetism of localized uranium moments below Tc 95 K and Kondo lattice behaviour at higher temperatures. We have found that ferromagnetism in both compounds is quenched at high pressure. In β-UB2C the Curie temperature continuously approaches zero at 2.95 GPa, where resistivity and specific heat reveal the behaviour similar to that observed in Ce-based antiferromagnets near quantum critical points. In UNiSi2 the Curie temperature decreases gradually to 25 K at 5.34 GPa. Above this pressure hysteretic phenomena appear in the temperature dependences of resistivity between 5 and 17 K, signalling a change in the magnetic order. No signature of magnetism was found above 5.5 GPa down to 1.15 K. Kondo lattice behaviour of resistivity with the enhanced residual resistivity is observed in UNiSi2 above 5.5 GPa. © Published under licence by IOP Publishing Ltd.

We report specific heat (C) and magnetization (M) of single crystalline Ce4Pt12Sn25 at temperature down to 50 mK and in fields up to 3 T. C/T exhibits a sharp anomaly at 180 mK, with a large jump in a Sommerfeld coefficient γ C/T of Δγ 30 J/molK2-Ce, which, together with corresponding cusp-like magnetization anomaly, indicate antiferromagnetic (AFM) ground state with Nel temperature TN 0.18 K. Numerical calculations based on Heisenberg model reproduce well zero field specific heat data, and point to a very small Kondo scale TK, clearly placing Ce4Pt12Sn25 in the weak exchange coupling J < Jc limit of the Doniac diagram. Magnetic field suppresses AFM state at H* 0.7 T, much more rapidly than indicated by theoretical calculations. © Published under licence by IOP Publishing Ltd.

We investigated the effect of electron and hole doping on the high-field low-temperature superconducting state in CeCoIn5 by measuring specific heat of CeCo (In1-x Mx) 5 with M=Sn, Cd, and Hg and x up to 0.33% at temperatures down to 0.1 K and fields up to 14 T. Although both Cd and Hg doping (hole doping) suppresses the zero-field Tc monotonically, Hc2 increases with small amounts of doping and has a maximum around x=0.2% (M=Cd). On the other hand, with Sn doping (electron doping) both zero-field Tc and Hc2 decrease monotonically. The critical temperature for the high-field low-temperature superconducting state correlates with Hc2 and Tc, which we interpret in support of the superconducting origin of this state. © 2010 The American Physical Society.

We investigated the effect of electron and hole doping on the high-field low-temperature superconducting state in CeCoIn5 by measuring specific heat of CeCo (In1-x Mx) 5 with M=Sn, Cd, and Hg and x up to 0.33% at temperatures down to 0.1 K and fields up to 14 T. Although both Cd and Hg doping (hole doping) suppresses the zero-field Tc monotonically, Hc2 increases with small amounts of doping and has a maximum around x=0.2% (M=Cd). On the other hand, with Sn doping (electron doping) both zero-field Tc and Hc2 decrease monotonically. The critical temperature for the high-field low-temperature superconducting state correlates with Hc2 and Tc, which we interpret in support of the superconducting origin of this state. © 2010 The American Physical Society.

We report specific heat (C) and magnetization (M) of single crystalline Ce4 Pt12 Sn25 at temperature down to ∼50 mK and in fields up to 3 T. C/T exhibits a sharp anomaly at 180 mK, with a large ΔC/T∼30 J/molCe K2, which, together with the corresponding cusplike magnetization anomaly, indicates an antiferromagnetic (AFM) ground state with a Néel temperature TN =180 mK. Numerical calculations based on a Heisenberg model reproduce both zero-field C and M data, thus placing Ce 4 Pt12 Sn25 in the weak exchange coupling J< Jc limit of the Doniach diagram, with a very small Kondo scale TK TN. Magnetic field suppresses the AFM state at H⊃ ≈0.7 T, much more effectively than expected from the Heisenberg model, indicating additional effects possibly due to frustration or residual Kondo screening. © 2010 The American Physical Society.

We show using neutron diffraction that the magnetic structure of CeRhIn4.85 Hg0.15 is characterized by a commensurate propagation vector (1/2,1/2,1/2). This is different from the magnetic structure in the parent compound CeRhIn5, which orders with an incommensurate propagation vector (1/2,1/2,0.297). The special relation between the commensurate magnetic mode and unconventional superconductivity has been shown previously for this class of heavy fermion superconductors. This work provides further evidence for the ubiquity of this antiferromagnetic mode. © 2009 The American Physical Society.

We studied the effect of impurity on the first order superconducting (SC) transition and the high field-low temperature (HFLT) SC state of CeCoIn5 by measuring the specific heat of CeCo(In1-xCdx)_{5} with x=0.0011, 0.0022, and 0.0033 and CeCo(In1-xHgx)_{5} with x=0.000 16, 0.000 32, and 0.000 48 at temperatures down to 0.1 K and fields up to 14 T. Cd substitution rapidly suppresses the crossover temperature T0, where the SC transition changes from second to first order, to T=0 K with x=0.0022 for H parallel[100], while it remains roughly constant up to x=0.0033 for H parallel[001]. The associated anomaly of the proposed FFLO state in Hg-doped samples is washed out by x=0.000 48, while remaining at the same temperature, indicating high sensitivity of that state to impurities. We interpret these results as supporting the nonmagnetic, possibly FFLO, origin of the HFLT state in CeCoIn5.

We report specific heat of CeCo (In0.975 Cd0.025)5 in magnetic field along basal plane. The superconducting transition is not sharp first order-like in high fields and the specific heat at field 12 T displays a sharp peak anomaly at 0.14 K inside the superconducting state. The anomaly is larger and sharper than that for the proposed Fulde-Ferell-Larkin-Ovchinnikov state in pure CeCoIn5. © 2007.

The physical properties of CeM (In1 - x Hgx)5 (M = Rh, Ir) including specific heat and magnetic susceptibility are reported. Two magnetic phases exist in CeRhIn (In1 - x Hgx)5 with some evidence of a change from incommensurate magnetic order to a commensurate structure near 10% nominal Hg substitution. In CeIr (In1 - x Hgx)5, an antiferromagnetic quantum critical point near x = 3 % (followed by robust long-range antiferromagnetism for x > 5 %) appears to be separated from superconductivity in CeIrIn5. The multitude of magnetic ground states observed in the CeM (In1 - x Hgx)5 materials is quite sensitive to doping and magnetic fields. © 2007.

The physical properties of CeM (In1 - x Hgx)5 (M = Rh, Ir) including specific heat and magnetic susceptibility are reported. Two magnetic phases exist in CeRhIn (In1 - x Hgx)5 with some evidence of a change from incommensurate magnetic order to a commensurate structure near 10% nominal Hg substitution. In CeIr (In1 - x Hgx)5, an antiferromagnetic quantum critical point near x = 3 % (followed by robust long-range antiferromagnetism for x > 5 %) appears to be separated from superconductivity in CeIrIn5. The multitude of magnetic ground states observed in the CeM (In1 - x Hgx)5 materials is quite sensitive to doping and magnetic fields. © 2007.

Thermal conductivity and specific heat were measured in the superconducting state of the heavy-fermion material Ce(1-x)La(x)CoIn5. With increasing impurity concentration x, the suppression of T(c) is accompanied by the increase in residual electronic specific heat expected of a d-wave superconductor, but it occurs in parallel with a decrease in residual electronic thermal conductivity. This contrasting behavior reveals the presence of uncondensed electrons coexisting with nodal quasiparticles. An extreme multiband scenario is proposed, with a d-wave superconducting gap on the heavy-electron sheets of the Fermi surface and a negligible gap on the light, three-dimensional pockets.