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

A. de la Torre; Q. Wang; Y. Masoumi; B. Campbell; J. V. Riffle; D. Balasundaram; P. M. Vora; J. P. C. Ruff; G. A. Fiete; S. M. Hollen; K. W. Plumb

doi:10.1038/s41567-025-02938-1

arXiv · 2407.07953

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

A. de la Torre·Q. Wang·Y. Masoumi·B. Campbell·J. V. Riffle·D. Balasundaram·P. M. Vora·J. P. C. Ruff·G. A. Fiete·S. M. Hollen·K. W. Plumb

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Abstract

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.

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A. de la Torre, Q. Wang, Y. Masoumi, B. Campbell, J. V. Riffle, D. Balasundaram, P. M. Vora, J. P. C. Ruff, G. A. Fiete, S. M. Hollen, K. W. Plumb. 2025-01-08. Dynamic phase transition into a mixed-CDW state in 1$T$-TaS$_2$ via a thermal quench. https://doi.org/10.1038/s41567-025-02938-1

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