We report the results of thermodynamic measurements in external magnetic field of the cubic Ce-based cage compounds Ce
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Abstract T 2Cd20(T = Ni,Pd). Our analysis of the heat-capacity data shows that the Γ7doublet is the ground state multiplet of the Ce3+ions. Consequently, for the Γ7doublet it can be theoretically shown that the Ruderman–Kittel–Kasuya–Yosida interaction between the localized Ce moments mediated by the conduction electrons, must vanish at temperatures much lower than the energy separating the ground state doublet from the first excited Γ8quartet. Our findings provide an insight as to why no long range order has been observed in these compounds down to temperatures in the milliKelvin range. -
Abstract CeOs4Sb12, a member of the skutterudite family, has an unusual semimetallic low-temperature
-phase that inhabits a wedge-like area of the fieldH —temperatureT phase diagram. We have conducted measurements of electrical transport and megahertz conductivity on CeOs4Sb12single crystals under pressures of up to 3 GPa and in high magnetic fields of up to 41 T to investigate the influence of pressure on the differentH –T phase boundaries. While the high-temperature valence transition between the metallic -phase and the -phase is shifted to higherT by pressures of the order of 1 GPa, we observed only a marginal suppression of the -phase that is found below 1 K for pressures of up to 1.91 GPa. High-field quantum oscillations have been observed for pressures up to 3.0 GPa and the Fermi surface of the high-field side of the -phase is found to show a surprising decrease in size with increasing pressure, implying a change in electronic structure rather than a mere contraction of lattice parameters. We evaluate the field-dependence of the effective masses for different pressures and also reflect on the sample dependence of some of the properties of CeOs4Sb12which appears to be limited to the low-field region. -
Global perspectives of the bulk electronic structure of URu 2 Si 2 from angle-resolved photoemission
Abstract Previous high-resolution angle-resolved photoemission (ARPES) studies of URu2Si2have characterized the temperature-dependent behavior of narrow-band states close to the Fermi level (
E F) at low photon energies near the zone center, with an emphasis on electronic reconstruction due to Brillouin zone folding. A substantial challenge to a proper description is that these states interact with other hole-band states that are generally absent from bulk-sensitive soft x-ray ARPES measurements. Here we provide a more globalk -space context for the presence of such states and their relation to the bulk Fermi surface (FS) topology using synchrotron-based wide-angle and photon energy-dependent ARPES mapping of the electronic structure using photon energies intermediate between the low-energy regime and the high-energy soft x-ray regime. Small-spot spatial dependence,f -resonant photoemission, Si 2p core-levels, x-ray polarization, surface-dosing modification, and theoretical surface slab calculations are employed to assist identification of bulk versus surface state character of theE F-crossing bands and their relation to specific U- or Si-terminations of the cleaved surface. The bulk FS topology is critically compared to density functional theory (DFT) and to dynamical mean field theory calculations. In addition to clarifying some aspects of the previously measured high symmetry Γ,Z andX points, incommensurate 0.6a * nested Fermi-edge states located alongZ –N –Z are found to be distinctly different from the DFT FS prediction. The temperature evolution of these states aboveT HO, combined with a more detailed theoretical investigation of this region, suggests a key role of theN -point in the hidden order transition. -
Abstract Spin-fluctuation-mediated unconventional superconductivity can emerge at the border of magnetism, featuring a superconducting order parameter that changes sign in momentum space. Detection of such a sign-change is experimentally challenging, since most probes are not phase-sensitive. The observation of a spin resonance mode (SRM) from inelastic neutron scattering is often seen as strong phase-sensitive evidence for a sign-changing superconducting order parameter, by assuming the SRM is a spin-excitonic bound state. Here we show that for the heavy fermion superconductor CeCoIn5, its SRM defies expectations for a spin-excitonic bound state, and is not a manifestation of sign-changing superconductivity. Instead, the SRM in CeCoIn5likely arises from a reduction of damping to a magnon-like mode in the superconducting state, due to its proximity to magnetic quantum criticality. Our findings emphasize the need for more stringent tests of whether SRMs are spin-excitonic, when using their presence to evidence sign-changing superconductivity.
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Free, publicly-accessible full text available August 1, 2024
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Recently, evidence for a conducting surface state (CSS) below 19 K was reported for the correlated
d -electron small gap semiconductor FeSi. In the work reported herein, the CSS and the bulk phase of FeSi were probed via electrical resistivity ρ measurements as a function of temperatureT , magnetic fieldB to 60 T, and pressureP to 7.6 GPa, and by means of a magnetic field-modulated microwave spectroscopy (MFMMS) technique. The properties of FeSi were also compared with those of the Kondo insulator SmB6to address the question of whether FeSi is ad -electron analogue of anf -electron Kondo insulator and, in addition, a “topological Kondo insulator” (TKI). The overall behavior of the magnetoresistance of FeSi at temperatures above and below the onset temperatureT S= 19 K of the CSS is similar to that of SmB6. The two energy gaps, inferred from the ρ(T ) data in the semiconducting regime, increase with pressure up to about 7 GPa, followed by a drop which coincides with a sharp suppression ofT S. Several studies of ρ(T ) under pressure on SmB6reveal behavior similar to that of FeSi in which the two energy gaps vanish at a critical pressure near the pressure at whichT Svanishes, although the energy gaps in SmB6initially decrease with pressure, whereas in FeSi they increase with pressure. The MFMMS measurements showed a sharp feature atT S≈ 19 K for FeSi, which could be due to ferromagnetic ordering of the CSS. However, no such feature was observed atT S≈ 4.5 K for SmB6.