Multiple Topological Phase Transitions Unveiling Gapless Topological Superconductivity in Magnet/Unconventional Superconductor Hybrid Platform

TL;DR

This paper presents a theoretical model showing how gapless topological superconductivity with Majorana edge modes can emerge in a 2D magnetic adatom array on an unconventional superconductor, revealing two topological phase transitions driven by exchange coupling.

Contribution

It introduces a novel framework for realizing gapless topological superconductivity in a 2D Shiba lattice with noncollinear spins on unconventional superconductors, identifying two distinct topological phase transitions.

Findings

Identification of two topological phase transitions driven by exchange coupling J.

Existence of a gapless topological phase hosting Majorana flat edge modes.

Insight into the pairing mechanisms leading to GTSC involving pseudo s-wave and p-wave components.

Abstract

We propose a theoretical framework for generating gapless topological superconductivity (GTSC) hosting Majorana flat edge modes (MFEMs) in the presence of a two-dimensional (2D) array of magnetic adatoms with noncollinear spin texture deposited on top of a unconventional superconductor. Our observations reveal two distinct topological phase transitions within the emergent Shiba band depending on the exchange coupling strength ($J$) between magnetic adatom spins and superconducting electrons: the first one designates transition from gapless non-topological to gapless topological phase at lower $J$, while the second one denotes transition from gapless topological to a trivial gapped superconducting phase at higher $J$. The gapless topological superconducting phase survives at intermediate values of $J$, hosting MFEMs. Further, we investigate the nature of the bulk effective pairings which indicate that GTSC appears due to the interplay between pseudo "$s$-wave" and pseudo "$p_{x}+p_y$" types of pairing. Consequently, our study opens a promising avenue for the experimental realization of GTSC in 2D Shiba lattice based on $d$-wave superconductors as a high-temperature platform.