Isostructural Mott Transition in 2D honeycomb antiferromagnet V${}_{0.9}$PS${}_3$

Abstract

We present the observation of an isostructural Mott insulator-metal transition in van-der-Waals honeycomb antiferromagnet V${}_{0.9}$PS${}_3$ through high-pressure x-ray diffraction and transport measurements. The MPX${}_3$ family of magnetic van-der-Waals materials (M denotes a first row transition metal and X either S or Se) are currently the subject of broad and intense attention, but the vanadium compounds have until this point not been studied beyond their basic properties. We observe insulating variable-range-hopping type resistivity in V${}_{0.9}$PS${}_3$, with a gradual increase in effective dimensionality with increasing pressure, followed by a transition to a metallic resistivity temperature dependence between 112 and 124 kbar. The metallic state additionally shows a low-temperature upturn we tentatively attribute to the Kondo Effect. A gradual structural distortion is seen between 26-80 kbar, but no structural change at higher pressures corresponding to the insulator-metal transition. We conclude that the insulator-metal transition occurs in the absence of any distortions to the lattice - an isostructural Mott transition in a new class of two-dimensional material, and in strong contrast to the behavior of the other MPX${}_3$ compounds.

12 pages, including appended supplementary section. Manuscript submitted to NPJ Quantum Materials