Structural, optical, and electrical properties of multiferroic GeV4S8 under high pressure*

Lacunar spinels, AM4X8 (A=Ga or Ge; M=V, Mo, Nb, or Ta; X=S or Se), constitute a distinct category of ternary chalcogenide compounds. One member in this category, GeV4S8, has attracted considerable attention because of its unique transport and magnetic properties. Previously and even in the recent, majority of the studies focused on the cooling effect on this material. Another approach, compression or high pressure, can cleanly tune and explore holistically the material's characteristics, but the investigation of GeV4S8 by using a high-pressure technique is rather scarce in the literature. In the present research, we utilized a diamond anvil cell integrated with high energy synchrotron x-ray diffraction, Raman spectroscopy, four-point probes to comprehensively characterize this material in terms of crystal structural transformation and conductivity variation induced by the compression. We tried to elucidate the mechanisms behind the phase transitions by Jahn-teller effect and the anisotropic changes in atomic configuration under high-pressure conditions.