Fragile surface zero-energy flat bands in three-dimensional chiral superconductors

TL;DR

This paper investigates the fragility of surface zero-energy flat bands in three-dimensional chiral superconductors with specific pairing symmetries, revealing their sensitivity to surface misorientation and spin-orbit interactions, and contrasting their behavior with other superconductors.

Contribution

It demonstrates the fragility of surface flat bands in chiral superconductors due to misorientation and Rashba spin-orbit interaction, and analyzes their impact on tunneling conductance and topological surface states.

Findings

Surface flat bands are fragile against misorientation angle.

Surface Rashba spin-orbit interaction suppresses flat bands.

Zero-bias conductance peaks are affected by flat band instabilities.

Abstract

We study surface zero-energy flat bands in three-dimensional chiral superconductors with $p_z (p_x +ip_y)^{\nu}$-wave pairing symmetry ($\nu$ is a nonzero integer), based on topological numbers and tunneling conductance. It is shown that the surface flat bands are fragile against (i) the misorientation angle and (ii) surface Rashba spin-orbit interaction. The fragility of (i) is specific to chiral SCs, whereas that of (ii) happens for general odd-parity SCs. We demonstrate that these flat band instabilities vanish or suppress a zero-bias conductance peak in a normal/insulator/superconductor junction, which behavior is clearly different from high-$T_c$ cuprates and noncentrosymmetric superconductors. By calculating the angle resolved conductance, we also discuss a topological surface state associated with the coexistence of line and point nodes.