Chiral Superconductivity in Thin Films of doped Bi$_2$Se$_3$

TL;DR

This paper investigates the conditions under which chiral superconductivity emerges in thin films of doped Bi$_2$Se$_3$, highlighting the influence of anisotropy and thickness, and predicts chiral Majorana modes in the 2D limit.

Contribution

It demonstrates that in strongly anisotropic or thin samples, chiral superconductivity is favored over nematic phases, and predicts boundary Majorana modes in the 2D limit.

Findings

Chiral phase favored in strongly anisotropic or thin samples.

Nematic phase stable in weakly anisotropic 3D systems.

Chiral Majorana modes exist at the boundary in the 2D limit.

Abstract

Recent experimental evidences point to rotation symmetry breaking superconductivity in doped Bi$_2$Se$_3$, where the relevant order parameter belongs to a two-component odd-parity representation $E_u$ of the crystal point group. The $E_u$ channel admits two possible phases, the chiral phase, that breaks time-reversal symmetry, and nematic phase, that well explains the reported rotation symmetry breaking. In weakly anisotropic three-dimensional systems the nematic phase is the stable one. We study the stability of the nematic phase versus the chiral phase as a function of the anisotropy of the system and the thickness of the sample and show that in the strongly anisotropic case or in thin slabs the chiral phases is favoured. For the extreme 2D limit composed by a single layer of Bi$_2$Se$_3$ the system hosts two chiral Majorana modes flowing at the boundary of the system.