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  1. Abstract CeOs 4 Sb 12 , a member of the skutterudite family, has an unusual semimetallic low-temperature L -phase that inhabits a wedge-like area of the field H —temperature T phase diagram. We have conducted measurements of electrical transport and megahertz conductivity on CeOs 4 Sb 12 single 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 different H – T phase boundaries. While the high-temperature valence transition between the metallic H -phase and the L -phase is shifted to higher T by pressures of the order of 1 GPa, we observed only a marginal suppression of the S -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 H -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 CeOs 4more »Sb 12 which appears to be limited to the low-field region.« less
    Free, publicly-accessible full text available April 1, 2023
  2. We have measured the superconducting penetration depth (T ) in the heavy-fermion/intermediate-valent superconducting alloy series Ce1−xYbxCoIn5 using a transverse-field muon spin relaxation to study the effect of intermediate-valent Yb doping on Fermi-liquid renormalization. From (T ) we determine the superfluid density ρs (T ) and find that it decreases continuously with increasing nominal Yb concentration x, i.e., with increasing intermediate valence. The temperature-dependent renormalization of the “normal” fluid density ρN (T ) = ρs (0) − ρs (T ) in both the heavy-fermion and intermediate valence limits is proportional to the temperature-dependent renormalization of the specific heat. This indicates that the temperature-dependent Fermiliquid Landau parameters of the superconducting quasiparticles entering the two different physical quantities are the same. These results represent an important advance in understanding of both intermediate valence and heavy-fermion phenomena in superconductors.