Structural phase transition, precursory electronic anomaly, and strong-coupling superconductivity in quasi-skutterudite (Sr1−xCax)3Ir4Sn13 and Ca3Rh4Sn13*Project supported by the National Natural Science Foundation of China (Grant Nos. 11674377 and 11634015), the National Key R&D Program of China (Grant Nos. 2017YFA0302904 and 2016YFA0300502), and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07020200). J. Y. is supported by the Youth Innovation Promotion Association of CAS. (July 2018)

• Record Type: Journal Article
• Authors: Luo 罗, Jun 军; Yang 杨, Jie 杰; Maeda, S; Li 李, Zheng 政; Zheng 郑, Guo-Qing 国庆
• Is Part Of: Chinese physics B. Volume 27:Number 7(2018)
• Publication Date: 2018-07
• Subjects: nuclear magnetic resonance -- antiferromagnetic fluctuation -- structural phase transition -- phase diagram; 74.25.nj -- 74.40.-n -- 74.25.Dw; Physics -- Periodicals; Physics; Periodicals; 530.05
• DOI: 10.1088/1674-1056/27/7/077401
• Languages: English
• ISSNs: 1674-1056

Abstract

Abstract : The interplay between superconductivity and structural phase transition has attracted enormous interest in recent years. For example, in Fe-pnictide high temperature superconductors, quantum fluctuations in association with structural phase transition have been proposed to lead to many novel physical properties and even the superconductivity itself. Here we report a finding that the quasi-skutterudite superconductors (Sr1− x Ca x )3 Ir4 Sn13 ( x = 0, 0.5, 1) and Ca3 Rh4 Sn13 show some unusual properties similar to the Fe-pnictides, through 119 Sn nuclear magnetic resonance (NMR) measurements. In (Sr1− x Ca x )3 Ir4 Sn13, the NMR linewidth increases below a temperature T * that is higher than the structural phase transition temperature T s . The spin-lattice relaxation rate (1/ T 1 ) divided by temperature ( T ), 1/ T 1 T and the Knight shift K increase with decreasing T down to T *, but start to decrease below T *, and followed by more distinct changes at T s . In contrast, none of the anomalies is observed in Ca3 Rh4 Sn13 that does not undergo a structural phase transition. The precursory phenomenon above the structural phase transition resembles that occurring in Fe-pnictides. In the superconducting state of Ca3 Ir4 Sn13, 1/ T 1 decays as exp(− Δ / k B T ) with a large gap Δ = 2.21 k B T c, yet without a Hebel–Slichter coherence peak, which indicates strong-coupling superconductivity. Our results provide new insight into the relationship between superconductivity and the electronic-structure change associated with structural phase transition.