Dynamic phase transition into a mixed-CDW state in 1$T$-TaS$_2$ via a thermal quench

• Main Authors: de la Torre, A, Wang, Q, Masoumi, Y, Campbell, B, Riffle, J. V, Balasundaram, D, Vora, P. M, Ruff, J. P. C, Fiete, G. A, Hollen, S. M, Plumb, K. W
• Format: Journal Article
• Language: English
• Published: 10.07.2024
• Subjects: Physics - Materials Science
• DOI: 10.48550/arxiv.2407.07953

Ultrafast light-matter interaction has emerged as a new mechanism to exert control over the macroscopic properties of quantum materials toward novel functionality. To date, technological applications of these non-thermal phases are limited by their ultrashort lifetimes and low-ordering temperatures. Among the most studied photoinduced metastable phases for their technological promise is the hidden metallic charge density wave (H-CDW) in the model correlated CDW compound 1$T$-TaS$_2$. Despite active study and engineering, the nature of the photoinduced H-CDW remains the subject of debate and is only accessible at cryogenic temperatures. Here, we stabilize the H-CDW phase at thermal equilibrium up to near-room temperature by accessing an intermediate mixed CDW order regime via thermal quenching. Using x-ray high dynamic range reciprocal space mapping (HDRM) and scanning tunneling spectroscopy (STS), we reveal the coexistence of commensurate (C) CDW and H-CDW domains below 180 K during cooling and below 210 K during warming. Our findings show that each order parameter breaks basal plane mirror symmetry with different chiral orientations and induces out-of-plane unit cell tripling in the H-CDW phase. Despite metallic domain walls and a finite density of states at zero bias observed via STS, bulk resistance remains insulating due to CDW stacking disorder. This study establishes the H-CDW as a thermally stable phase and introduces a new mechanism for switchable metallic behavior in thin flakes of 1$T$-TaS$_2$ and similar materials with competing order phases.