443 / 2019-03-07 11:31:31

Pressure-induced phase transition to non-layered structure and the enhanced superconductivity in 1T-TaS2

1T-TaS2; Pressure; Enhanced superconductivity; Phase transition; Electron–phonon coupling

全体主题 > High Pressure Physics and Materials Science

We have investigated the structural phase transition and superconductivity of 1T-TaS2 up to ~100 GPa via in situ high pressure X-ray experiments and electrical transport measurements. The superconductivity behavior have persisted up to ~100 GPa. The trend of Tc below 25 GPa in our measurements is in line with the previous research. Tc reaches the peak of ~ 6 K at ~ 20 GPa and then drops to ~ 4.2 K at around 40 GPa. Upon further increasing the pressure, Tc enhanced again and reaches ~ 6.6 K at 98.8 GPa. Synchrotron x-ray diffraction measurements reveal that 1T-TaS2 transform to a layered distorted 1T’ phase at 25.7 GPa and then to a non-layered structure at around 45.0 GPa. Considering the impact of different transmission mediums applied in two measurements, we attribute the change of the trend of Tc at ~20 GPa and ~40 GPa to the structure transition. The “non-layered” structure presents more excellent superconductivity than the layered 1T or distorted 1T’ structure. Upon further increasing the pressure, the “non-layered” structure undergoes a transformation to a tetragonal I4/mmm structure at 56.9 GPa, which is completely finished at 81.4 GPa. However, disregard the structural phase transition, Tc proceeds to increase, indicating that the superconductivity after ~40 GPa is closely related to the connection between layers. The strong electron–phonon coupling accounts for the superconductivity of the high pressure non-layered I4/mmm structure.