Investigation of superconducting and normal-state properties of the filled-skutterudite system PrPt4Ge12−xSbx

We report a study of the superconducting and normal-state properties of the filled-skutterudite system PrPt4Ge12−xSbx . Polycrystalline samples with Sb concentrations up to x = 5 were synthesized and investigated by means of x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements. We observed a suppression of superconductivity with increasing Sb substitution up to x = 4, above which no signature of superconductivity was observed down to 140 mK. The Sommerfeld coefficient, γ , of superconducting specimens decreases with increasing x up to x = 3, suggesting that superconductivity may depend on the density of electronic states in this system. The specific heat for x = 0.5 exhibits an exponential temperature dependence in the superconducting state, reminiscent of a nodeless superconducting energy gap. We observed evidence for a weak “rattling” mode associated with the Pr ions, characterized by an Einstein temperature ΘE ∼ 60 K for 0 ≤ x ≤ 5; however, the rattling mode may not play any role in suppressing superconductivity

Effect of thermally excited lattice vibrations on the thermodynamic stability of tungsten ditellurides WTe2 under high pressure: A first-principles investigation

The thermodynamic stability as a function of pressure and temperature of three WTe2 polytypes, i. e., Td, 1T , and 2H phases, is examined using first-principles calculations, where the temperature-dependent contributions, arising particularly from the lattice vibrations, are derived from the quasiharmonic approximation. We find that the critical transition pressure to the 2H phase increases almost linearly with increasing temperature. Through the inspection of the phonon density of states, 2H-WTe2 is dynamically stable not only at high pressure, but also at zero pressure, indicating possible existence of 2H-WTe2 also at ambient conditions. On the other side, our results demonstrate that, at relevant temperature and pressure, the thermodynamic stability of 1T-WTe2 is comparable to that of Td-WTe2, and further analysis reveals substantial similarities in terms of structural behavior between Td-WTe2 and 1T-WTe2. These findings suggest not only that the two polytypes are likely to coexist in practical samples of WTe2 due probably to grains/regions either with tiny difference in stress, for example, or with different growth history, but also that the designation of 1T , having been regularly used to described the compound under pressure in the literature, might actually be a mixture of Td and 1T polytypes, whose WTe2 layers laterally slide via low transition barrier induced probably by the applied pressure, resulting in the splitting of (101) and (113) peaks as observed in the diffraction experiments.Funding Agencies|Thailand Toray Science Foundation (TTSF); Ratchadaphiseksomphot Endowment Fund, Chulalongkorn UniversityChulalongkorn University [CU-GR_62_66_23_26]; Ratchadaphiseksomphot Endowment Fund, Chulalongkorn UniversityChulalongkorn University; Grants for Development of New Faculty Staff and the Research Fund for DPST Graduate [003/2015]; Institute for the Promotion of Teaching Science and Technology (IPST), Thailand; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Swedish Foundation [FFL 15-0290]; Swedish Research Council (VR)Swedish Research Council [2019-05403]; Knut and Alice Wallenberg FoundationKnut &amp; Alice Wallenberg Foundation [KAW-2018.0194]</p

Search for multipolar instability in URu2Si2 studied by ultrasonic measurements under pulsed magnetic field

The elastic properties of URu2Si2 in the high magnetic field region above 40 T, over a wide temperature range from 1.5 to 120 K, were systematically investigated by means of high-frequency ultrasonic measurements. The investigation was performed at high magnetic fields to better investigate the innate bare 5f-electron properties, since the unidentified electronic thermodynamic phase of unknown origin, the so-called "hidden order" (HO), and associated hybridization of conduction and f electrons (c-f hybridization) are suppressed at high magnetic fields. From the three different transverse modes we find contrasting results; both the Gamma(4)(B-2g) and Gamma(5)(E-g) symmetry modes C-66 and C-44 show elastic softening that is enhanced above 30 T, while the characteristic softening of the Gamma(3)(B-1g) symmetry mode (C-11 - C-12)/2 is suppressed in high magnetic fields. These results underscore the presence of a hybridization-driven Gamma(3)(B-1g) lattice instability in URu2Si2. However, the results from this work cannot be explained by using existing crystalline electric field schemes applied to the quadrupolar susceptibility in a local 5f(2) configuration. Instead, we present an analysis based on a band Jahn-Teller effect