Ultrafast collective dynamics unveils emergent quantum state in 1T-TaS2
Date：11-04-2025 Print
Exploring and revealing new quantum states has always been one of the frontier topics in condensed matter physics. Ultrafast spectroscopy has revealed many mysteries in condensed matter physics due to its unique capability in achieving extremely high temporal resolution. Layered charge density wave (CDW) materials provide an ideal research platform for revealing the emerging physical phenomena. 1T-TaS2 as a typical CDW material undergoes a continuous CDW phase transition during the heating and cooling processes. Many investigations mainly focused on the CCDW-NCCDW phase transition, and very few investigations have been conducted within the commensurate CDW phase below 180K. To date only very few investigations have reported the behavior of 1T-TaS2 in the temperature range of CCDW phase, suggesting possible existence of a quantum spin liquid state.
Recently, Professor ZHAO Jimin Group (the SF10i Group) of the Institute of Physics, Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics, in collaboration with Professor ZHOU Yi from T06 Group, Professor CHEN Xianhui Group from the University of Science and Technology of China, and Professor ZHENG Liu from the Center for Advanced Research of Tsinghua University, have conducted the ultrafast spectroscopy investigation of 1T-TaS2, from which an unknown novel quantum state in 1T-TaS2 is discovered (Figure 1).
Experimentally, Professor ZHAO Jimin Group used ultrafast spectroscopy to detect the low temperature ultrafast dynamics of 1T-TaS2, and detected six time-domain coherent oscillation modes in the temperature domain for the commensurate CDW, among which the 2.47 THz mode is the amplitude mode (AM) of the CDW. Using the high resolution of ultrafast spectroscopy, it is found that the temperature dependence of the frequency, full width at half maximum (FWHM) and integrated amplitude the AM has a crossover at 65 K: each physical quantity satisfies the conventional T2 relation at 65-200 K. However, a completely different T3.56 relation is found at temperatures below 65K (Figure 2). Based on the analysis of the experimental results, the authors identify the state below 65K as a new emerging quantum state owing to the couplings among the multi-degree-of-freedom. The investigation deepens our understanding of CDW materials and also provides new perspectives for exploring the cutting-edge areas such as quantum spin liquid.
The research results were recently published in the Proceedings of the National Academy of Sciences with the title "Emergent quantum state unveiled by ultrafast collective dynamics in 1T-TaS2" [PNAS 122, e2406464122 (2025)]. It is selected as the cover story by the Chinese magazine Physics, volume 3 of 2025.
This work was supported by the National Key R&D Program of China, National Natural Science Foundation of China, Chinese Academy of Sciences, and Beijing Natural Science Foundation.
The article link is: https://doi.org/10.1073/pnas.2406464122
Fig. 1 Emergent quantum state in 1T-TaS2 unveiled by ultrafast collective dynamics.
Fig. 2 Temperature dependence of the integrated amplitude, FWHM, and frequency of all coherent modes.
Contact:
Institute of Physics
ZHAO Jimin
Email：jmzhao@iphy.ac.cn
Key words:
Ultrafast spectroscopy; Emergent quantum state; Ultrafast dynamics; CDW; Coherent Phonon
Abstract:
The amplitude mode (AM) of the CDW in 1T-TaS2 was discovered to exhibit an unusual T3.56 dependence below 65K beyond a conventional T2 temperature dependence above 65K through ultrafast spectroscopy. This phase crossover reveals a new quantum state emerging, providing a new understanding of the CDW materials and non-equilibrium correlated quantum states, as well as shining light on quantum spin liquids.
