Novel anisotropic spin singlet pairings in Cu$_x$Bi$_2$Se$_3$ and Bi$_2$Te$_3$

TL;DR

This paper investigates novel anisotropic spin singlet pairings in Bi$_2$X$_3$ (X=Se, Te), revealing two unique pairings with surface states that could be detected experimentally, and explores their origin from Coulomb interactions.

Contribution

It identifies new anisotropic spin singlet pairings in Bi$_2$X$_3$ and analyzes their surface states and pairing mechanisms, advancing understanding of superconductivity in these materials.

Findings

Two novel pairings show nontrivial surface Andreev bound states.

Surface states could produce zero bias conductance peaks.

Antiferromagnetic superexchange favors spin singlet pairing.

Abstract

Possible anisotropic spin singlet pairings in Bi$_2$X$_3$ (X is Se or Te) are studied. Among six pairings compatible with the crystal symmetry, two novel pairings show nontrivial surface Andreev bound states, which form flat bands and could produce zero bias conductance peak in measurements like point contact spectroscopy. By considering purely repulsive short range Coulomb interaction as the pairing mechanism, the dominant superexchange terms are all antiferromagnetic, which would usually favor spin singlet pairing in Bi$_2$X$_3$. Mean field analyses show that the interorbital pairing interaction favors a mixed spatial-parity anisotropic pairing state, and one pairing channel with zero energy surface states has a sizable component. The results provide important new information for future experiments.