Non-Abelian and Abelian descendants of vortex spin liquid: fractional quantum spin Hall effect in twisted MoTe$_2$

Abstract: The recent experimental observation of a potential fractional quantum spin Hall (FQSH) state in the twisted MoTe$2$ system has sparked theoretical explorations at total filling $\nu_T=1$ of a pair of $C=\pm 1$ Chern bands from the two spins (locked to valley). One intriguing candidate is a vortex spin liquid (VSL), which can be viewed as an exciton version of composite fermi liquid (CFL). The VSL insulator is incompressible in the charge channel, while compressible in the spin channel. Here we investigate fully gapped descendants of the VSL phase at the total filling $\nu_T=\nu{\uparrow}+\nu_{\downarrow}=1$. At zero magnetization, a non-Abelian state with both FQSH and thermal Hall effect emerges from weak $p+ip$ pairing of the neutral Fermi surface, hosting 12 anyons (up to addition of physical electron) including two independent Ising anyons separately carrying charge and spin. Strong pairing leads to a Z$_4$ topological order with only FQSH effect. At non-zero magnetization $m=2S_z$, there is a Jain sequence of magnetic plateaus with $m=\frac{1}{p}, p \in Z$, exhibiting both half FQSH effect and spin fractional quantum Hall effect (SFQH). Our work highlights the VSL's potential as a parent state to organize numerous FQSH insulators with non-trivial inter-valley correlations at $\nu_T=1$. The quantized FQSH behavior remains robust even in the presence of ferromagnetism, thanks to the spin-charge separation nature inherent in the parent VSL phase. Future experimental investigations are crucial to validate or rule out spontaneous magnetization and time reversal symmetry breaking.