# Robust odd-parity superconductivity in the doped topological insulator Nb$_x$Bi$_2$Se$_3$

## TL;DR

This study demonstrates that the doped topological superconductor Nb$_x$Bi$_2$Se$_3$ exhibits robust odd-parity superconductivity with symmetry-protected point nodes, even under high disorder levels, supporting the nematic $E_u$ pairing state.

## Contribution

It provides experimental evidence of robust odd-parity superconductivity in Nb$_x$Bi$_2$Se$_3$ under disorder, highlighting the stability of the nematic $E_u$ pairing state.

## Key findings

- Superconductivity persists despite high disorder levels.
- The transition temperature $T_c$ decreases with disorder without saturation.
- The penetration depth follows a $T^2$ power law indicating point nodes.

## Abstract

We present resistivity and magnetization measurements on proton-irradiated crystals demonstrating that the superconducting state in the doped topological superconductor Nb$_x$Bi$_2$Se$_3$ (x = 0.25) is surprisingly robust against disorder-induced electron scattering. The superconducting transition temperature $T_c$ decreases without indication of saturation with increasing defect concentration, and the corresponding scattering rates far surpass expectations based on conventional theory. The low-temperature variation of the London penetration depth $\Delta\lambda(T)$ follows a power law ($\Delta\lambda(T)\sim T^2$) indicating the presence of symmetry-protected point nodes. Our results are consistent with the proposed robust nematic $E_u$ pairing state in this material.