Emergent quantum state unveiled by ultrafast collective dynamics in 1<i>T</i>-TaS<sub>2</sub>.

Hasaien, Jiazila; Wu, Yanling; Shi, Mengzhu; Zhai, Yanni; Wu, Qiong; Liu, Zheng; Zhou, Yi; Chen, Xianhui et al. · Proc Natl Acad Sci U S A · 2025

basic_science · Level V

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Abstract

Charge density wave (CDW) material 1<i>T</i>-TaS<sub>2</sub> was proposed as a quantum spin liquid candidate, on which a cluster Mott insulator comes into being below the transition temperature. We report an experimental ultrafast generation and detection of the coherent amplitude mode (AM) of its CDW state. A salient feature emerges: The coherent CDW mode AM exhibits an unusual <i>T</i><sup>3.56</sup> temperature dependence below 65 K, in addition to the <i>T</i><sup>2</sup> temperature dependence observed in the 65 to 200 K range. This behavior suggests the enhancement of in-gap electronic excitations below 65 K and the emergence of a new phase of matter. Consequently, the intriguing quantum state leads to a crossover. Our investigation provides insights into understanding the interplay among various degrees of freedom in quantum materials.