Tunable zero-energy Dirac and Luttinger nodes in a two-dimensional topological superconductor

TL;DR

This paper explores how tunable zero-energy Dirac and Luttinger nodes emerge in a two-dimensional topological superconductor with spin-triplet pairing, influenced by spin-orbit coupling and external parameters, revealing rich quasiparticle spectra.

Contribution

It introduces a model where Dirac and Luttinger nodes in a 2D topological superconductor are tunable via external controls like gate voltage, highlighting the formation, movement, and merging of nodes.

Findings

Dirac nodes are pinned to zero energy by particle-hole symmetry.

Nodes can move and merge as the order parameter or spin-orbit coupling vary.

Special parameter values lead to quadratic band-touching spectra.

Abstract

Cooper pairing in ultrathin films of topological insulators, induced intrinsically or by proximity effect, can produce an energetically favorable spin-triplet superconducting state. The spin-orbit coupling acts as an SU(2) gauge field and stimulates the formation of a spin-current vortex lattice in this superconducting state. Here we study the Bogoliubov quasiparticles in such a state and find that the quasiparticle spectrum consists of a number of Dirac nodes pinned to zero energy by the particle-hole symmetry. Some nodes are "accidental" and move through the first Brillouin zone along high-symmetry directions as the order parameter magnitude or the strength of the spin-orbit coupling are varied. At special parameter values, nodes forming neutral quadruplets merge and become gapped out, temporarily producing a quadratic band-touching spectrum. All these features are tunable by controlling the order parameter magnitude via a gate voltage in a heterostructure device. In addition to analyzing the spectrum at the mean-field level, we briefly discuss a few experimental signatures of this spectrum.