Tunable spin and valley excitations of correlated insulators in $\Gamma$-valley moir\'e bands

TL;DR

This study uses twisted double bilayer WSe$_2$ to explore tunable correlated insulator phases, revealing spin-polarized states, valley control, and a novel metal-insulator transition driven by electric fields.

Contribution

It demonstrates experimental control over spin and valley degrees of freedom in $ m extit{ extbf{ extGamma}}$-valley moiré bands, revealing new correlated phases and transitions.

Findings

Identification of charge-ordered phases at multiple moiré fillings

Observation of spin-polarized ground states with quasiparticle excitations

Electric field-induced metal-insulator transition between $ m extit{ extGamma}$- and $K$-valley bands

Abstract

Moir\'e superlattices formed from transition metal dichalcogenides (TMDs) have been shown to support a variety of quantum electronic phases that are highly tunable using applied electromagnetic fields. While the valley character of the low-energy states dramatically affects optoelectronic properties in the constituent TMDs, this degree of freedom has yet to be fully explored in moir\'e systems. Here, we establish twisted double bilayer WSe$_2$ as an experimental platform to study electronic correlations within $\Gamma$-valley moir\'e bands. Through a combination of local and global electronic compressibility measurements, we identify charge-ordered phases at multiple integer and fractional moir\'e band fillings $\nu$. By measuring the magnetic field dependence of their energy gaps and the chemical potential upon doping, we reveal spin-polarized ground states with novel spin polaron quasiparticle excitations. In addition, an applied displacement field allows us to realize a new mechanism of metal-insulator transition at $\nu = -1$ driven by tuning between $\Gamma$- and $K$-valley moir\'e bands. Together, our results demonstrate control over both the spin and valley character of the correlated ground and excited states in this system.