Yazar "Maple, M. Brian" seçeneğine göre listele

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    Investigation of superconducting and normal-state properties of the filled-skutterudite system PrPt4Ge12-xSbx
    (Amer Physical Assoc, 2016) Jeon, Inho; Huang, Kevin; Yazıcı, Duygu; Kanchanavatee, Noravee; White, B. D.; Ho, Pei-Chun; Jang, Sooyoung; Pouse, Naveen; Maple, M. Brian
    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, gamma, 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 Theta(E) similar to 60 K for 0 <= x <= 5; however, the rattling mode may not play any role in suppressing superconductivity.
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    Multiband superconductivity in the correlated electron filled skutterudite system Pr1-xCexPt4Ge12
    (Amer Physical Soc, 2016) Zhang, S.; Singh, Yogesh P.; Adhikari, Rupendra Bahadur; Zhang, S.; Huang, Kevin; Yazıcı, Duygu; Jeon, Inho; Maple, M. Brian; Dzero, Maxim; Almasan, Carmen C.
    Studies of superconductivity in multiband correlated electronic systems have become one of the central topics in condensed-matter and materials physics. In this paper, we present the results of thermodynamic measurements on the superconducting filled skutterudite system Pr1-xCexPt4Ge12 (0 <= x <= 0.2) to investigate how substitution of Ce at Pr sites affects superconductivity. We find that an increase in Ce concentration leads to a suppression of the superconducting transition temperature from T-c similar to 7.9 K for x = 0 to T-c similar to 0.6 K for x = 0.14. Our analysis of the specific-heat data for x <= 0.07 reveals that superconductivity must develop in at least two bands: the superconducting order parameter has nodes on one Fermi pocket and remains fully gapped on the other. Both the nodal and nodeless gaps decrease, with the nodal gap being suppressed more strongly upon Ce substitution. Ultimately, the higher-Ce-concentration samples (x > 0.07) display a nodeless gap only.
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    Structure, magnetization, specific heat, and microwave properties of KxFe2-ySe2
    (IOP Publishing Ltd, 2016) Yazıcı, Duygu; Başaran, Ali Cemil; Ramirez, Juan Gabriel; Schuller, Ivan K.; Maple, M. Brian
    Temperature-dependent magnetization, specific heat, and magnetic field modulated microwave spectroscopy (MFMMS) measurements were performed on single crystals of KxFe2-ySe2. Magnetization measurements yield a superconducting transition temperature (T-c) of similar to 30 K, with a diamagnetic shielding fraction of nearly 90%. Specific heat measurements revealed a 'jump' at T-c, Delta C/T vertical bar T-c, of about 6.8 +/- 1 mJ mol(-1) K-2, consistent with bulk superconductivity in KxFe2-ySe2. Moreover, MFMMS measurements detect the superconductivity of KxFe2-ySe2. with a peak with an onset at T-c(mu) similar to 28 K, close to the values of T-c determined from the magnetization and specific heat measurements. The presence and the shape of the low temperature MFMMS signal could be ascribed to a complex dissipation mechanism and percolative superconductivity.
  • Küçük Resim
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    Superconducting and normal state properties of the systems La1-xMxPt4Ge12 (M = Ce, Th)
    (Amer Physical Soc, 2016) Huang, Kevin; Yazıcı, Duygu; White, Bryan D.; Jeon, Inho; Breindel, Alexander J.; Pouse, Naveen; Maple, M. Brian
    Electrical resistivity, magnetization, and specific heat measurements were performed on polycrystalline samples of the filled-skutterudite systems La1?xMxPt4Ge12 (M = Ce, Th). Superconductivity in LaPt4Ge12 was quickly suppressed with Ce substitution and no evidence for superconductivity was found down to 1.1 K for x > 0.2. Temperature-dependent specific heat data at low temperatures for La1?xCexPt4Ge12 show a change from power-law to exponential behavior, which may be an indication for multi-band superconductivity in LaPt4Ge12. A similar crossover was observed in the Pr1?xCexPt4Ge12 system. However, the suppression rates of the superconducting transition temperatures, Tc(x), in the two systems are quite disparate, indicating a difference in the nature of superconductivity, which is conventional in LaPt4Ge12 and unconventional in PrPt4Ge12. In comparison, a nearly linear and smooth evolution of Tc with increasing Th was observed in the La1?xThxPt4Ge12 system, with no change of the superconducting energy gap in the temperature dependence of the specific heat, suggesting similar types of superconductivity in both the LaPt4Ge12 and ThPt4Ge12 compounds.