Interplay of Rashba spin-orbit coupling and Coulomb interaction in topological spin-triplet excitonic condensates

TL;DR

This paper explores how Rashba spin-orbit coupling and Coulomb interactions work together to stabilize topological spin-triplet excitonic condensates in two-dimensional systems, revealing a transition to topologically nontrivial states with potential real-world applications.

Contribution

It provides a microscopic mechanism showing how Rashba SOC induces topological excitonic condensates and identifies conditions for their realization in specific material systems.

Findings

Weak Coulomb interaction with Rashba SOC leads to spin-momentum locking and semimetal behavior.

Stronger Coulomb interaction stabilizes spin-triplet excitonic condensates.

Increasing valence-band SOC causes a transition to a topological EC with Chern number 2.

Abstract

The cooperative effect of Rashba spin-orbit coupling (SOC) and Coulomb attraction in stabilizing topological spin-triplet excitonic condensates (ECs) in two-dimensional electron-hole systems in external magnetic field is investigated by using an unrestricted Hartree-Fock approach combined with the random-phase approximation. At weak electron-hole Coulomb interaction, the intraband Rashba SOC induces spin-momentum locking and topological semimetal behavior, while stronger interaction stabilizes spin-triplet ECs. Increasing the valence-band SOC drives a transition from a topologically trivial EC with coexisting spin-up and spin-down components to a topological spin-up EC only with quantized Chern number $C=2$. The dynamical excitonic susceptibility reveals a soft spin-up triplet mode acting as the precursor of the condensate. These results establish a microscopic mechanism for Rashba SOC-induced topological ECs and suggest realistic situations for their realization in noncentrosymmetric Janus transition-metal dichalcogenides and twisted van der Waals heterostructures.