Bulk superconducting phase with a full energy gap in the doped topological insulator Cu_xBi_2Se_3

TL;DR

This study provides evidence of a fully-gapped, strong-coupling superconducting state in Cu_xBi_2Se_3, a doped topological insulator, with indications of unconventional pairing and significant mass enhancement, advancing the understanding of topological superconductivity.

Contribution

The paper reports the first specific heat measurements confirming a fully-gapped superconducting state in Cu_xBi_2Se_3, suggesting unconventional pairing mechanisms.

Findings

Specific heat anomaly indicates a fully-gapped superconducting state

Evidence of strong-coupling superconductivity in Cu_xBi_2Se_3

Large effective mass suggests significant electron correlation

Abstract

The superconductivity recently found in the doped topological insulator Cu_xBi_2Se_3 offers a great opportunity to search for a topological superconductor. We have successfully prepared a single-crystal sample with a large shielding fraction and measured the specific-heat anomaly associated with the superconductivity. The temperature dependence of the specific heat suggests a fully-gapped, strong-coupling superconducting state, but the BCS theory is not in full agreement with the data, which hints at a possible unconventional pairing in Cu_xBi_2Se_3. Also, the evaluated effective mass of 2.6m_e (m_e is the free electron mass) points to a large mass enhancement in this material.