Controversy over large proximity induced s wave like pairing from a d wave superconductor

TL;DR

This paper investigates the proximity effect in heterostructures of high-temperature cuprate superconductors and topological insulators, finding that large induced s-wave gaps are unlikely and questioning the nature of observed gaps.

Contribution

It provides a mean field analysis of Bi2Sr2CaCu2O8+δ and Bi2Se3 heterostructures, challenging claims of large proximity-induced s-wave gaps and highlighting the need for further interface studies.

Findings

Large proximity-induced s-wave gaps are unlikely.

Observed gaps may not be purely superconducting coherence gaps.

Further interface and bulk studies are needed.

Abstract

Proximity effect is used to generate effective topological superconductor by placing strong spin orbit interacting metals with superconducting materials, aiming to produce Majorana zero modes useful for topologically protected quantum computations. In recent experiments high $T_c$ material $\text{Bi}_2\text{Sr}_2\text{CaCu}_2\text{O}_{8+\delta}$ is put in contact with a few quintuple layer thick $\text{Bi}_2\text{Se}_3$, and conflicting experimental results are reported. We use standard mean field approach to study this heterostructure, and find it is unlikely to have large proximity induced superconducting gap. The claimed observed s-wave gap might not be purely superconducting coherence gap despite its seemingly correct temperature dependence. Further study on the proximity induced bulk coherence gap and the band structure at the interface should shed light on this issue.