From Semiconducting to Metallic: Jahn-Teller-Induced Phase Transformation in Skyrmion Host GaV4S8

Lacunar spinels, GaM4X8 (M = V, Nb, Mo, Ta, W; X = S, Se, Te), constitute a rare class of compounds with multiferroic properties. Recently, one member of this family, GaV4S8, received global attention due to the Neel-type skyrmions discovered in this material. Previous investigations strongly indicate the important role of the structure behind the multi-ferroicity, for example, the strong impact of ferroelectric transition on the exchange interactions at similar to 40 K. Inspired by the delicate entanglement of lattice, spin, and charge degrees of freedom, in the present work, we aimed to use pressure to alter the structure and thus change the material's properties to establish the inter-relation between the structural, optical, and electrical properties for a better understanding of this skyrmion host material. Upon this objective, in situ high-pressure measurements of single crystal/powder Xray diffraction, electrical conductivity, and Raman spectroscopy were carried out by using a diamond anvil cell. These studies revealed the pressure-induced structural transformation from cubic to orthorhombic, along with a transition from semiconductor to metallic state in GaV4S8. The phase changes coincide with the variation in the optical property in this material explored by Raman spectra. We also determined the bulk modulus of the two phases of GaV4S8 by fitting the data set of unit cell volumes against pressure with the second-order birth-Murnaghan equation of state, and explained the mechanisms of phase transitions by means of the Jahn-Teller effect and the anisotropic changes in bonding lengths during compression.

Automated summary

The rare class of compounds Lacunar spinels, GaM4X8 (M = V, Nb, Mo, Ta, W; X = S, Se, Te), exhibit multiferroic properties, with GaV4S8 attracting global attention due to the discovery of Neel-type skyrmions. Utilizing pressure to alter the structure, researchers observed a transition from cubic to orthorhombic structure and from semiconductor to metallic state in GaV4S8. The study also explored the relationship between structural, optical, and electrical properties, shedding light on the mechanisms of phase transitions in the material.