Models of Superconducting Cu:Bi2Se3: single versus two-band description

TL;DR

This paper develops a pseudospin basis for Bi2Se3 to analyze superconducting states, comparing single-band and two-band models, revealing unusual momentum dependencies and clarifying surface state behaviors.

Contribution

It introduces a pseudospin basis for Bi2Se3's normal state and compares single-band and two-band superconducting models, highlighting novel momentum dependencies.

Findings

Unusual momentum dependence in odd parity states.

Surface state behaviors explained by d(k) forms.

Single-band and two-band models show notable differences.

Abstract

Starting from a model Hamiltonian for the normal state of the topological insulator Bi2Se3, we construct a pseudospin basis for the single-particle wavefunctions. Considering weak superconducting pairing near the Fermi surface, we express the recently proposed superconducting order parameters for Cu doped Bi2Se3 in this basis. For the odd parity states, the d-vectors specifying the order parameter can have unusual momentum dependence for certain parameter regimes. Some peculiar results in the literature for surface states are discussed in light of the forms of these d(k)'s. Properties of the even parity states are also illuminated using this pseudospin basis. Results from this single-band description are compared with those from the full two-band model.