Universal giant spin Hall effect in moire metal

Abstract

While moiré 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 $4\frac{e}{4\ddot{I}€}$ at $5.09^{\circ }$ to $10\frac{e}{4\ddot{I}€}$ 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 $6\frac{e}{4\ddot{I}€}$ at $5.09^{\circ }$ to $17\frac{e}{4\ddot{I}€}$ at $3.89^{\circ }$. For prototypical moiré metals like twisted NbX${}_2$, we identify a record SHC of $-17\frac{e}{4\ddot{I}€}$ (-5200 $(\hslash /e)S/cm$ in 3D units), surpassing all known bulk materials. These results establish moiré 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.

4.5+ 27 pages, 4+ 24 figures