Journal
NANO RESEARCH
Volume 14, Issue 4, Pages 1162-1166Publisher
TSINGHUA UNIV PRESS
DOI: 10.1007/s12274-020-3166-1
Keywords
charge density wave 1T-TaS2; layer-dependent; phase transition stiffness; ultrafast carrier dynamics
Categories
Funding
- National Key Research and Development Program of China [2017YFA0205000, 2017YFA0303600, 2016YFA0200701]
- National Natural Science Foundation of China [21425310, 21790353, 21721002, 21822502, 21673058]
- Strategic Priority Research Program of Chinese Academy of Sciences [XDB36000000, XDB30000000]
- Key Research Program of Frontier Sciences of CAS [QYZDB-SSW-SYS031]
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Study shows that 1T-TaS2 nanoflakes undergo a phase transition from commensurate CDW to nearly commensurate CDW state around 210K, with the phase transition stiffness depending on thickness. Thinner nanoflakes exhibit a smaller phase transition stiffness due to increased fluctuations, inhibiting the nucleation and growth of discommensurations. The results suggest that carrier dynamics could be an efficient method to study quantum phase transition in correlated materials.
Novel physical properties emerge when the thickness of charge density wave (CDW) materials is reduced to the atomic level, owing to the significant modification of the electronic band structure and correlation effects. Here, we investigate the layer-dependent CDW phase transition and evolution of the nonequilibrium state of 1T-TaS2 nanoflakes using pump-probe spectroscopy. Both the low-energy single-particle and collective excitation relaxations exhibit sharp changes at similar to 210 K, indicating a phase transition from commensurate CDW to nearly commensurate CDW state. The single particle process reveals that the phase transition stiffness (PTS) is thickness-dependent. Moreover, a small PTS is observed in thin nanoflakes, which is attributed to the reduced thickness that increases the fluctuation and inhibits the nucleation and growth of discommensurations. In addition, the phase mode vanishes when the discommensuration network appears. Our results suggest that the carrier dynamics could be an efficient operational approach to measuring the quantum phase transition in correlated materials.
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