Optical control over topological Chern number in moir\'e materials

TL;DR

This paper demonstrates all-optical switching of spin-valley states in twisted MoTe2, enabling dynamic control over topological phases and paving the way for optically tunable topological quantum devices.

Contribution

It introduces a method to optically reverse the spin-valley orientation in moiré materials with flat Chern bands, achieving non-thermal control of topological order.

Findings

Optical switching of ferromagnetic spin states at zero magnetic field.

Demonstration of dynamic reversal of topological phases.

Potential for creating optically tunable topological quantum circuits.

Abstract

Controlling quantum matter with light offers a promising route to dynamically tune its many-body properties, ranging from band topology to superconductivity. However, achieving such optical control for strongly correlated electron systems in the steady-state has remained elusive. Here, we demonstrate all-optical switching of the spin-valley degree of freedom of itinerant ferromagnets in twisted MoTe2 homobilayers. This system uniquely features flat valley-contrasting Chern bands and exhibits a range of strongly correlated phases at various moir\'e lattice fillings, including Chern insulators and ferromagnetic metals. We show that the spin-valley orientation of all of these phases can be dynamically reversed by resonantly exciting the attractive polaron transition with circularly-polarized light. These findings not only constitute the first direct evidence for non-thermal switching of a ferromagnetic spin state at zero magnetic field, but also demonstrate the possibility of dynamical control over topological order parameter, paving the way for all-optical generation of chiral edge modes and topological quantum circuits.