Synergistic chemical and optical switching of chiral symmetry breaking in 1T-TaS$_2$

TL;DR

This study demonstrates how combining chemical doping with ultrafast optical pulses enables efficient, non-thermal switching of chiral charge density wave states in 1T-TaS$_2$, revealing a phonon-mediated mechanism.

Contribution

It introduces a novel approach of chemical and optical synergy to control chiral symmetry breaking in quantum materials.

Findings

Ti doping stabilizes coexisting chiral domains.

Optical excitation induces asymmetric switching between chiral domains.

Switching occurs on a timescale of about 2 THz, involving a transient domain-wall state.

Abstract

Optical control of symmetry-breaking quantum phases is a central goal in quantum materials, yet deterministic switching is often hindered by the stability of single-domain ground states. The chiral structure of the charge density wave (CDW) in 1T-TaS$_2$ provides a natural platform for such control, but the pristine material remains locked in a single chirality. Here we show that combining chemical doping with femtosecond optical excitation enables efficient direct and non-thermal switching of the chiral CDW state and reveal its microscopic mechanism. Ti substitution stabilizes a ground state with coexisting chiral domains, creating a tunable energy landscape for optical manipulation. Femtosecond photoexcitation then induces asymmetric and anisotropic switching from dominant to minority chiral domains, characterized by in-plane domain growth and a redistribution toward an achiral configuration. The switching occurs on a timescale comparable to a coherent phonon oscillation ($\sim$2 THz), revealing a phonon-mediated pathway that proceeds through a transient domain-wall state. Our work establishes a new paradigm for synergistic control of chiral order parameters using chemical and ultrafast optical tuning in quantum materials.