Robust two-gap strong coupling superconductivity associated with low-lying phonon modes in pressurized Nb5Ir3O superconductors  

作　　者：Bosen Wang Yaoqing Zhang Shuxiang Xu Jin-Guang Cheng 王铂森;张尧卿;徐淑香;Kento Ishigaki;Kazuyuki Matsubayashi;程金光;Hideo Hosono;Yoshiya Uwatoko(Beijing National Laboratory for Condensed Matter Physics and Institute of Physics,Chinese Academy of Sciences,Beijing 100190,China;Institute for Solid State Physics,University of Tokyo,Kashiwanoha 5-1-5,Kashiwa,Chiba 277-8581,Japan;Materials Research Center for Element Strategy,Tokyo Institute of Technology,Yokohama 226-8503,Japan;Songshan Lake Materials Laboratory,Dongguan 523808,China)

机构地区：[1]Beijing National Laboratory for Condensed Matter Physics and Institute of Physics,Chinese Academy of Sciences,Beijing 100190,China [2]Institute for Solid State Physics,University of Tokyo,Kashiwanoha 5-1-5,Kashiwa,Chiba 277-8581,Japan [3]Materials Research Center for Element Strategy,Tokyo Institute of Technology,Yokohama 226-8503,Japan [4]Songshan Lake Materials Laboratory,Dongguan 523808,China

出　　处：《Chinese Physics B》2019年第10期215-221,共7页中国物理B（英文版）

基　　金：Project supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0305700 and 2018YFA0305800);JSPS Kakenhi(Grant No.17H06153);the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant Nos.XDB25000000 and QYZDB-SSW-SLH013);the National Natural Science Foundation of China(Grant No.11574377);Beijing Natural Science Foundation,China(Grant No.Z190008);IOP Hundred-Talent Program,China(Grant No.Y7K5031×61);the Youth Promotion Association,Chinese Academy of Sciences(Grant No.2018010)

摘　　要：We report robust superconducting state and gap symmetry of Nb5Ir3O via electrical transport and specific heat measurements. The analysis of specific heat manifests that Nb5Ir3O is a strongly coupled superconductor with ΔC/γnTc ~ 1.91 and double s-wave superconducting gaps of 2ΔL(0)/kBTc ~ 6.56 and 2ΔS(0)/kBTc ~ 2.36 accounting for 90% and 10%,respectively. The(Cp-γnT)/T^3 vs. T plot shows a broad peak at ~ 23 K, indicating phonon softening and the appearance of low-lying phonon mode associated with the interstitial oxygen. This behavior explains the monotonic increase of Tc in Nb5Ir3O(1-δ)by strengthening the electron-phonon coupling and enlarging the density of states at Fermi level. The Hall coefficient is temperature independent below 200 K, and changes its sign from positive to negative above 250 K, suggesting that carrier is across the hole-to electron-dominant regions and the multi-band electronic structures. On warming, the resistivity shows a gradual crossover from T^2-to T^3-dependence at a critical temperature T^*, and a broad peak at a temperature Tp. The reduced Tc under pressure is linearly correlated with lattice parameters c/a ratio and Tp, suggesting the important phonon contributions in Nb5Ir3O as a phonon-medicated superconductor. Possible physical mechanisms are proposed.We report robust superconducting state and gap symmetry of Nb5Ir3O via electrical transport and specific heat measurements. The analysis of specific heat manifests that Nb5Ir3O is a strongly coupled superconductor with ?C/γnTc ～ 1.91 and double s-wave superconducting gaps of 2?L（0）/kBTc ～ 6.56 and 2?S（0）/kBTc ～ 2.36 accounting for 90% and 10%,respectively. The（Cp-γnT）/T3 vs. T plot shows a broad peak at 23 K, indicating phonon softening and the appearance of low-lying phonon mode associated with the interstitial oxygen. This behavior explains the monotonic increase of Tc in Nb5Ir3O（1-δ）by strengthening the electron–phonon coupling and enlarging the density of states at Fermi level. The Hall coefficient is temperature independent below 200 K, and changes its sign from positive to negative above 250 K, suggesting that carrier is across the hole-to electron-dominant regions and the multi-band electronic structures. On warming, the resistivity shows a gradual crossover from T2-to T3-dependence at a critical temperature T*, and a broad peak at a temperature Tp. The reduced Tc under pressure is linearly correlated with lattice parameters c/a ratio and Tp, suggesting the important phonon contributions in Nb5Ir3O as a phonon-medicated superconductor. Possible physical mechanisms are proposed.

关 键 词：new SUPERCONDUCTOR high-pressure effect STRONGLY coupled SUPERCONDUCTOR 

分 类 号：O4[理学—物理]