Topological spin-up triplet excitonic condensation in two-dimensional electron-hole systems

Abstract

We investigate topological spin-up triplet excitonic condensation and its competition with other stabilities in a two-dimensional interacting electron-hole system taking into account Rashba spin-orbit coupling and external magnetic fields. Using an unrestricted Hartree-Fock approach, we self-consistently evaluate spin-selective excitonic condensate order parameters and the Chern number. The ground state phase diagram in the dependence on magnetic field and Coulomb interaction shows a spin-up triplet excitonic condensate (EC) with a nonzero Chern number, emerging uniquely away from the topologically trivial singlet and spin-down triplet EC regions. Strong spin-polarized triplet excitonic fluctuations preceding the condensation are further revealed through the signatures of the dynamical excitonic susceptibility spectra. Our results establish a class of topological quantum phases driven by excitonic coherence and suggest a realistic pathway to its realization in a distorted Janus monolayer of transition metal dichalcogenides or some twisted van der Waals heterostructures.

Figures (3)

• Figure 1: Magnitude of EC order parameters $|\Delta_{\sigma\sigma'}|$ (first two rows) and Chern number $C$ (last row) as functions of magnetic field $H$ at different values of Coulomb interaction $U$ (left column) and as functions of $U$ at some values of $H$ (right column).
• Figure 2: Ground state phase diagram of the 2D electron-hole system in the $H-U$ plane. EC can be stabilized either in singlet (magenta), spin-up triplet (red), or spin-up and spin-down triplet coexistence (green). The SM state is marked in light-green, and the SC state is marked either in light-blue (SC$_1$) or in light-orange (SC$_2$). The topological nontrivial region is bounded by the blue solid line.
• Figure 3: The imaginary part of the dynamical excitonic susceptibility functions at zero momentum $\text{Im} \chi^{\sigma\sigma'}(\omega)$ for all spin configurations at $U=4.5$ and $H=0.5$ (a) and for spin-up triplet only with different values of $H$ at $U=4.5$ (b) and at $U=1$ (c).