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Following our recent discovery of superconductivity in YbRh 2 Si 2 at 2 mK, nearly coinciding with a hybrid electronic–nuclear magnetic moment ordering (Schuberth et al. in Science 351:485, 2016), we re-analyzed previous data on the magnetic susceptibility of CeCu 6 at ultra-low temperatures. We found that there is a direct analogy between the magnetic susceptibilities of both compounds which raises the question if there is the same hybrid transition in CeCu 6 , possibly also followed by superconductivity. Data taken some 20 years ago by groups in Garching and at Cornell University revealed an antiferromagnetic transition around 3 mK and further anomalies around 0.5 mK, very similar to the case of YbRh 2 Si 2 . If the above speculation is correct, it would suggest that superconductivity is a general phenomenon, occurring even in a heavy-fermion compound like CeCu 6 which for a long time was considered as "non-ordering." [ABSTRACT FROM AUTHOR]

Insulating states can be topologically nontrivial, a well-established notion that is exemplified by the quantum Hall effect and topological insulators. By contrast, topological metals have not been experimentally evidenced until recently. In systems with strong correlations, they have yet to be identified. Heavy-fermion semimetals are a prototype of strongly correlated systems and, given their strong spin-orbit coupling, present a natural setting to make progress. Here, we advance a Weyl-Kondo semimetal phase in a periodic Anderson model on a noncentrosymmetric lattice. The quasiparticles near the Weyl nodes develop out of the Kondo effect, as do the surface states that feature Fermi arcs. We determine the key signatures of this phase, which are realized in the heavy-fermion semimetal Ce3Bi4Pd3. Our findings provide the much-needed theoretical foundation for the experimental search of topological metals with strong correlations and open up an avenue for systematic studies of such quantum phases that naturally entangle multiple degrees of freedom. [ABSTRACT FROM AUTHOR]

Cerium-based ternary compounds CeNi 2 Cd 20 and CePd 2 Cd 20 do not exhibit long-range order down to millikelvin temperature range. Given the large separation between Ce ions which significantly reduces the super-exchange interactions and vanishingly small Ruderman-Kittel-Kasuya-Yosida interaction, here we show that nodal superconductivity mediated by the valence fluctuations must be a ground state in these materials. We propose that the critical temperature for the superconducting transition can be significantly increased by applying hydrostatic pressure. We employ an extended periodic Anderson lattice model which includes the long-range Coulomb interactions between the itinerant electrons as well as the local Coulomb interaction between the predominantly localized and itinerant electrons to compute a critical temperature of the superconducting transition. Using the slave-boson approach we show that fluctuations mediated by the repulsive electron-electron interactions lead to the emergence of d -wave superconductivity., (Creative Commons Attribution license.)

Abstract: We performed the elastic neutron scattering experiments on the mixed compounds , and found that doping Co into dramatically changes the antiferromagnetic (AF) structure. The incommensurate AF state with the propagation vector of observed in pure is suppressed with increasing x, and new AF states with an incommensurate and a commensurate modulations simultaneously develop near the AF quantum critical point: . These results suggest that the AF correlations with the and modulations enhanced in the intermediate Co concentrations may play a crucial role in the evolution of the superconductivity observed above . [Copyright &y& Elsevier]

Abstract: The penetration depth in the filled-skutterudite heavy-fermion superconductor PrOs4Sb12 has been measured using transverse-field muon spin rotation (TF-). It is found to be temperature-independent at low temperatures, consistent with a nonzero gap for quasiparticle excitations. In contrast, radiofrequency (RF) measurements yield a stronger temperature dependence of , indicative of point nodes in the gap. A discrepancy is found at low temperatures. This may be due to mechanisms that modify the vortex-state field distribution, or to the surface scattering which breaks pairs in an odd-parity superconductor. Alternatively, it may be a matter of field orientation of nodal gap structure in the measurements. [Copyright &y& Elsevier]

Abstract: We report on extensive neutron diffraction on single crystalline to determine the antiferromagnetic order in the regime with low Ge content, initially called A phase due to the unknown origin of the magnetic order. Starting from the alloy we followed the magnetic order to lower Ge concentrations and to pure . For all Ge concentrations an incommensurate magnetic order with a propagation vector close to is observed. The magnetic order is determined by the nesting properties of the Fermi surface. [Copyright &y& Elsevier]

We propose a method which explicitly takes into account the strength of on-site Coulomb interactions to calculate the effective mass of carrier fermions in the intermetallics of f and non- f atoms. Calculations of a number of heavy-fermion systems show a satisfactory trend of variation of effective carrier fermion mass. [ABSTRACT FROM AUTHOR]

Abstract: The heavy-fermion compound orders antiferromagnetically below the Néel temperature . The magnetic order can be suppressed either by applying a magnetic field of (for ) or by replacing Si with Ge. The latter is equivalent to a negative lattice pressure. In search of a field-induced quantum phase transition, we studied the disappearance of magnetic order in at , using specific-heat and resistivity measurements. Apart from a slightly enhanced specific heat and resistivity at , no signs for quantum criticality could be identified down to 0.35K. Our data indicate that belongs to the heavy-fermion compounds in which the magnetic field gradually reduces the amount of antiferromagnetic order until the magnetic entropy vanishes continuously at and the system changes smoothly to a field-polarized paramagnet. [Copyright &y& Elsevier]

The low temperature properties of CeCu6−xAux show different behavior at the quantum phase transition depending on how the long-range antiferromagnetic order is suppressed. Tuning by hydrostatic pressure p results in a temperature dependence of the specific heat C(T) and the electrical resistivity ρ(T) as C/T=a ln(T0/T) and ρ≈ρ0+A′T, while C/T=γ0−a′T0.5 and ρ≈ρ0+A″T1.5 when tuned by applying a magnetic field B. The magnetic (p,T) and (B,T) phase diagrams as inferred from specific heat, electrical resistivity and neutron diffraction measurements are distinctly different. These findings suggest that the spectra of the low-lying magnetic fluctuations near these quantum phase transitions differ. [Copyright &y& Elsevier]

We have theoretically analysed DC resistivity ( ρ ) in the Kondo-lattice materials using the powerful memory function formalism. The complete temperature evolution of ρ is investigated using the Wölfle-Götze expansion of the memory function. The resistivity in this model originates from spin-flip magnetic scattering of conduction s -electron off the quasi-localized d or f electron spins. We find the famous resistivity upturn in lower temperature regime ( k B T ≪ μ d ), where μ d is the effective chemical potential of d -electrons. In the high temperature regime ( μ d ≪ k B T ) we discover that resistivity scales as cube root of T (ρ∝T32). Our results are in reasonable agreement with the experimental results reported in the literature., (© 2020 IOP Publishing Ltd.)

Insulating states can be topologically nontrivial, a well-established notion that is exemplified by the quantum Hall effect and topological insulators. By contrast, topological metals have not been experimentally evidenced until recently. In systems with strong correlations, they have yet to be identified. Heavy-fermion semimetals are a prototype of strongly correlated systems and, given their strong spin-orbit coupling, present a natural setting to make progress. Here, we advance a Weyl-Kondo semimetal phase in a periodic Anderson model on a noncentrosymmetric lattice. The quasiparticles near the Weyl nodes develop out of the Kondo effect, as do the surface states that feature Fermi arcs. We determine the key signatures of this phase, which are realized in the heavy-fermion semimetal Ce 3 Bi 4 Pd 3 Our findings provide the much-needed theoretical foundation for the experimental search of topological metals with strong correlations and open up an avenue for systematic studies of such quantum phases that naturally entangle multiple degrees of freedom., Competing Interests: The authors declare no conflict of interest., (Copyright © 2017 the Author(s). Published by PNAS.)

An interference of heavy-fermion superconductivity (SC) and antiferromagnetism (AFM) has been studied in the framework of the periodic Anderson model with the superexchange interaction between localized electrons. It has been shown that pressure-induced energy change of the localized states leads to modifying antiferromagnetic and superconducting order parameters. Conditions have been found for the coexistence of SC and AFM in the model. Theoretical results of the pressure effects on the ground state character of the heavy-fermion systems are in good agreement with experimental data for a rare-earth intermetallic compound CeRhIn. The divergence of the effective electron mass produced by suppressing the long-range antiferromagnetic order has also been analyzed in the same framework. [ABSTRACT FROM AUTHOR]

Abstract: We report on the low-temperature dc magnetic susceptibility of in very small fields and 1mT. For , i.e. for the quantum critical concentration, we confirm the anomalous exponent of the susceptibility along the easy c-direction, with observed previously in moderate fields (see, A. Schröder, et al., Nature 407 (2000) 351). However, below 240mK we see a clear additional contribution to . At the lowest measuring temperature , the ratio of the susceptibility anisotropy is weaker than at higher T where the ratio is 10:2:1. This is caused by a steeper increase of and as compared to . [Copyright &y& Elsevier]

Abstract: We investigate the thermodynamic and transport properties of YbNiSi3, previously shown to order antiferromagnetically at 5.1K by Avila et al., and YbNiGe3 which does not show magnetic order down to 1.85K. The magnetic phase diagram of YbNiSi3 is determined from magnetoresistance and specific-heat measurements. [Copyright &y& Elsevier]

Abstract: We report on a comparative study of the low-temperature magnetoresistance and Hall resistance of for with magnetic field along the easy direction. The data are discussed in terms of the metamagnetic transition manifest in , and of the anomalous Hall effect and bandstructure effects of the heavy-quasiparticle bands affecting . [Copyright &y& Elsevier]