Link between superconductivity and a Lifshitz transition in intercalated Bi$_2$Se$_3$

TL;DR

This study links superconductivity in intercalated Bi$_2$Se$_3$ to a Lifshitz transition, revealing a change in Fermi surface topology associated with the emergence of superconductivity, using ARPES and SdH measurements.

Contribution

It provides direct experimental evidence connecting Lifshitz transition and superconductivity in intercalated Bi$_2$Se$_3$, highlighting the role of Fermi surface topology.

Findings

Fermi surface is an open cylinder with higher carrier density.

Superconductivity correlates with the appearance of a quasi-2D Fermi surface.

Despite low Hall number, the actual carrier density is much higher.

Abstract

Topological superconductivity is an exotic phase of matter in which the fully gapped superconducting bulk hosts gapless Majorana surface states protected by topology. Intercalation of copper, strontium or niobium between the quintuple layers of the topological insulator Bi$_2$Se$_3$ increases the carrier density and leads to superconductivity that is suggested to be topological. Here we study the electronic structure of strontium-intercalated Bi$_2$Se$_3$ using angle resolved photoemission spectroscopy (ARPES) and Shubnikov-de Haas (SdH) oscillations. Despite the apparent low Hall number of $\sim2 \times 10 ^{19}$cm$^{-3}$, we show that the Fermi surface is shaped as an open cylinder with a larger carrier density of $\sim 10 ^{20}$cm$^{-3}$. We suggest that superconductivity in intercalated Bi$_2$Se$_3$ emerges with the appearance of a quasi-2D open Fermi surface.