Universal giant spin Hall effect in moire metal

Abstract

While moir\'e phenomena have been extensively studied in low-carrier-density systems such as graphene and semiconductors, their implications for metallic systems with large Fermi surfaces remain largely unexplored. Using GPU-accelerated large-scale ab-initio quantum transport simulations, we investigate spin transport in two distinct platforms: twisted bilayer MoTe$_2$ (semiconductor, from lightly to heavily doping) and NbX$_2$ ($X$ = S, Se; metals). In twisted MoTe$_2$, the spin Hall conductivity (SHC) evolves from $4\tfrac{e}{4\pi}$ at $5.09^\circ$ to $10\tfrac{e}{4\pi}$ at $1.89^\circ$, driven by the emergence of multiple isolated Chern bands. Remarkably, in heavily doped metallic regimes--without isolated Chern bands--we observe a universal amplification of the spin Hall effect from Fermi surface reconstruction under long-wavelength potential, with the peak SHC tripling from $6\tfrac{e}{4\pi}$ at $5.09^\circ$ to $17\tfrac{e}{4\pi}$ at $3.89^\circ$. For prototypical moir\'e metals like twisted NbX$_2$, we identify a record SHC of $-17\tfrac{e}{4\pi}$ (-5200 $(\hbar / e)S/cm$ in 3D units), surpassing all known bulk materials. These results establish moir\'e engineering as a powerful strategy for enhancing spin-dependent transport, and advancing ab-initio methodologies to bridge atomic-scale precision with device-scale predictions in transport simulations.