Tuning between a fractional topological insulator and competing phases at $\nu_\mathrm{T}=2/3$

Abstract

We study a spinful, time-reversal symmetric lowest Landau level model for a flatband quantum spin Hall system at total filling fraction $\nu_\mathrm{T}=2/3$. Such models are relevant, e.g. for spin-valley locked moir\'e transition metal dichalcogenides. The opposite Chern number of the two spins hinders the formation of a quantum Hall ferromagnet, instead favouring other phases. We study the phase diagram in dependence on different short-range Haldane pseudopotentials $V_m$ and uncover several phases: A fractional topological insulator, a phase separated state, a spin-polarized fractional quantum Hall state, and the partially particle-hole transformed Halperin (111) state. The effect of the pseudopotentials $V_m$ depends on the parity of $m$, the relative angular momentum.