Transport evidence for three dimensional topological superconductivity in doped $\beta$-PdBi$_2$

TL;DR

This study provides transport evidence that K-doped β-PdBi₂ is a three-dimensional topological superconductor with Majorana surface states, marking a significant step in identifying materials with topological superconductivity.

Contribution

The paper reports the discovery of 3D topological superconductivity in doped β-PdBi₂, demonstrating a transition from trivial to topological superconducting states upon doping.

Findings

Signatures of Majorana surface states in doped β-PdBi₂

Evidence of odd-parity pairing in the bulk

Undoped β-PdBi₂ is a trivial superconductor

Abstract

Interest in topological states of matter exploded over a decade ago with the theoretical prediction and experimental detection of three-dimensional topological insulators, especially in bulk materials that can be tuned out of it by doping. However, their superconducting counterpart, the time-reversal invariant three-dimensional topological superconductor, has evaded discovery thus far. In this work, we provide transport evidence that K-doped $\beta$-PdBi$_2$ is a 3D time-reversal-invariant topological superconductor. In particular, we find signatures of Majorana surface states protected by time-reversal symmetry--the hallmark of this phase--in soft point-contact spectroscopy, while the bulk system shows signatures of odd-parity pairing via upper-critical field and magnetization measurements. Odd-parity pairing can be argued, using existing knowledge of the band structure of $\beta$-PdBi$_2$, to result in 3D topological superconductivity. Moreover, we find that the undoped system is a trivial superconductor. Thus, we discover $\beta$-PdBi$_2$ as a unique material that, on doping, can potentially undergo an unprecedented topological quantum phase transition in the superconducting state.