Magnetic order on a topological insulator surface with warping and proximity-induced superconductivity

TL;DR

This paper investigates the magnetic order on a topological insulator surface influenced by warping and superconductivity, revealing a skyrmion lattice phase with potential for topological superconductivity and controllable magnetic properties.

Contribution

It identifies a skyrmion lattice magnetic ground state on TI surfaces due to warping and Hubbard interactions, and explores how proximity-induced superconductivity affects this phase.

Findings

Skyrmion lattice magnetic order forms for strong interactions.

Magnetic order preserves C3 symmetry and has nonzero skyrmion charge.

Proximity to a superconductor can engineer a topological superconductor.

Abstract

We determine the nature of the magnetic order on the surface of a topological insulator (TI) which develops due to hexagonal warping and the resulting Fermi surface (FS) nesting in the presence of a repulsive Hubbard interaction. For this purpose we investigate the spin susceptibility and derive a Landau theory to compare the different accessible phases. For a nearly hexagonal FS and sufficiently strong interaction the magnetic ground state is formed by a skyrmion lattice, i.e., by a superposition of three helical spin density waves which preserves C$_3$ symmetry. The magnetic ground state is topologically nontrivial with a nonzero skyrmion charge, which can be stabilized and controlled by an applied magnetic field. By bringing the TI in proximity to a conventional superconductor one can engineer a C$_3$-symmetric topological superconductor. We explore the modification of the phase diagram as well as the mutual influence between the skyrmion structure and a multipolar distribution of supercurrents, which can provide information about the underlying skyrmion charge.