# Evidence for singular-phonon-induced nematic superconductivity in a topological superconductor candidate Sr$_{0.1}$Bi$_2$Se$_3$

## TL;DR

This study reveals highly anisotropic phonons in Sr0.1Bi2Se3, suggesting a singular electron-phonon interaction that likely induces exotic p-wave nematic superconductivity, advancing understanding of topological superconductors.

## Contribution

It provides evidence that anisotropic phonons induce unconventional superconductivity in Sr0.1Bi2Se3, highlighting a novel electron-phonon coupling mechanism for topological superconductivity.

## Key findings

- Anisotropic phonons observed along [001] direction.
- Large electron-phonon coupling at small momenta.
- Supports electron-phonon interaction inducing exotic pairing.

## 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.