Effect of local Coulomb interaction on Majorana corner modes: weak and strong correlation limits

TL;DR

This paper investigates how local Coulomb interactions influence Majorana corner modes in higher-order topological superconductors, revealing phase diagram modifications and the persistence of Majorana modes under strong correlations.

Contribution

It provides a comprehensive analysis of Coulomb interaction effects on HOTSCs in both weak and strong regimes, including mean-field and effective Hamiltonian approaches.

Findings

Coulomb repulsion widens the topologically nontrivial phase.

Boundary effects induce a crossover to spin-dependent solutions.

Majorana corner modes persist even at infinite repulsion.

Abstract

Here we present an analysis of the evolution of Majorana corner modes realizing in a higher-order topological superconductor (HOTSC) on a square lattice under the influence of local Coulomb repulsion. The HOTSC spectral properties were considered in two regimes: when the intensities of many-body interactions are either weak or strong. The weak regime was studied using the mean-field approximation with self-consistent solutions carried out both in the uniform case and taking into account of the boundary of the finite square-shaped system. It is shown that in the uniform case the topologically nontrivial phase on the phase diagram is widened by the Coulomb repulsion. The boundary effect, resulting in an inhomogeneous spatial distribution of the correlators, leads to the appearance of the crossover from the symmetric spin-independent solution to the spin-dependent one characterized by a spontaneously broken symmetry. In the former the corner states have energies that are determined by the overlap of the excitation wave functions localized at the different corners. In the latter the corner excitation energy is defined by the Coulomb repulsion intensity with a quadratic law. The crossover is a finite size effect, i.e. the larger the system the lesser the critical value of the Coulomb repulsion. In the strong repulsion regime we derive the effective HOTSC Hamiltonian in the atomic representation and found a rich variety of interactions induced by virtual processes between the lower and upper Hubbard subbands. It is shown that Majorana corner modes still can be realized in the limit of the infinite repulsion. Although the boundaries of the topologically nontrivial phase are strongly renormalized by Hubbard corrections.