Abstract
The MPX3 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 for low-dimensional magnetism and transport and also for novel device and technological applications, but the vanadium compounds have until this point not been studied beyond their basic properties. We present the observation of an isostructural Mott insulator–metal transition in van-der-Waals honeycomb antiferromagnet V0.9PS3 through high-pressure x-ray diffraction and transport measurements. We observe insulating variable-range-hopping type resistivity in V0.9PS3, 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 and 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 MPX3 compounds.
Highlights
Layered two-dimensional van-der-Waals materials are currently the subject of broad and detailed research.[1]
We have demonstrated a continuous transition from insulating to metallic states in 2D antiferromagnet V0.9PS3
No change in the crystal lattice was observed in the vicinity of the transition, in contrast to previous results on FePS3 and MnPS3 where the insulator–metal transition is accompanied by a dramatic first-order structural phase transition: a collapse of the interplanar spacing
Summary
Layered two-dimensional van-der-Waals materials are currently the subject of broad and detailed research.[1]. They can be mechanically exfoliated as with graphene and have been shown to maintain their magnetic ordering down to monolayer thickness.[24,25] These materials are all insulating—they exhibit an exponentially increasing resistivity with decreasing temperature—and can be understood as p-type semiconductors[9] and as Mott insulators.[26] Recent works have demonstrated Mott insulator–metal transitions in MnPS3 and FePS326–28 and superconductivity in FePSe3.29 A large focus in 2D materials research is and has been into the transition metal dichalcogenide systems,[30,31,32,33] leading to the discovery of many new states—MPX3 are a new family in the same vein, with rich magnetic and correlated-electron properties to explore.
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