Evidence for singular-phonon-induced nematic superconductivity in a topological superconductor candidate Sr0.1Bi2Se3

Jinghui Wang,Xiangang Wan,A Schneidewind,Sergey Y Savrasov,Seiko Ohira-Kawamura,Jinsheng Wen,Youtian Zhang,Song Bao,Zhengwei Cai,Zhen Ma,P Čermák,Shichao Li,Kejing Ran,Kenji Nakajima

doi:10.1038/s41467-019-10942-2

Abstract

Superconductivity mediated by phonons is typically conventional, exhibiting a momentum-independent s-wave pairing function, due to the isotropic interactions between electrons and phonons along different crystalline directions. Here, by performing inelastic neutron scattering measurements on a superconducting single crystal of Sr0.1Bi2Se3, a prime candidate for realizing topological superconductivity by doping the topological insulator Bi2Se3, we find that there exist highly anisotropic phonons, with the linewidths of the acoustic phonons increasing substantially at long wavelengths, but only for those along the [001] direction. This observation indicates a large and singular electron-phonon coupling at small momenta, which we propose to give rise to the exotic p-wave nematic superconducting pairing in the MxBi2Se3 (M = Cu, Sr, Nb) superconductor family. Therefore, we show these superconductors to be example systems where electron-phonon interaction can induce more exotic superconducting pairing than the s-wave, consistent with the topological superconductivity.

Highlights

Superconductivity mediated by phonons is typically conventional, exhibiting a momentumindependent s-wave pairing function, due to the isotropic interactions between electrons and phonons along different crystalline directions
There are some cases where phonons may play some role in the unconventional superconductivity, for example, in YBa2Cu3O7−x, but how the electron-phonon coupling is related to the presumable d-wave pairing is not clear at the moment[2,3,4,5]
Sr0.1Bi2Se3 is a member of the MxBi2Se3 (M=Cu, Sr, Nb) family, which become superconducting by doping the topological insulator Bi2Se314–38

Summary

Introduction

Superconductivity mediated by phonons is typically conventional, exhibiting a momentumindependent s-wave pairing function, due to the isotropic interactions between electrons and phonons along different crystalline directions. Examining the electron-phonon interaction experimentally is the key to the understanding of the superconducting pairing mechanism in the MxBi2Se3 (M=Cu, Sr, Nb) superconductor family.

Results

Conclusion