Dynamic control of macroscopic phases via thermal quench in 1T-TaS₂

In materials with competing order parameters, quenching across a phase transition can lead to the system being trapped in a long-lived metastable phase, even if it is not the global free-energy minimum. Examples of this phenomenology can be found over multiple energies and length scales, from the evolution of the known Universe to supercooled liquids [1]. 1T-TaS₂, a layered dichalcogenide, is a unique platform for studying dynamic phase transitions in quantum materials [2]. Upon quenching 1T-TaS₂ after excitation with an ultrafast laser pulse, a low-temperature metallic metastable phase (H-CDW) emerges [3], which is different from any of the charge density wave (CDW) phases characterizing its thermodynamic phase diagram. I will show that a new metastable insulating phase with similar scattering signatures to the H-CDW [4] can be stabilized by intermediate quenching rates [5]. I will discuss the implications of this new phase in the controversy surrounding the presence of Mott physics and the role of c-axis correlations [6] in the equilibrium ground state of 1T-TaS₂.