Insulator-Metal Transition in Two-dimensional Mott Insulator NiPS₃ under pressure

NiPS₃ crystallizes in a monoclinic C2/m structure at ambient pressure. The Ni ions form a honeycomb lattice, and each layer is isolated between two layers of S and P triangles (PS₃), separated by van der Waals (vdW) gaps. Below 155 K, NiPS₃ orders anti-ferromagnetically with the magnetic moment directed mostly along the c axis.¹ There is a prediction that pressure-induced Mott insulator to metal transition (IMT) might be accompanied by the |S_Z| = 1 to |S_Z| = 1/2 state without changing crystal structure.² The electronically-driven IMT suggests that NiPS₃ is a promising material for ultrafast resistivity switching. We performed electrical resistance and XRD measurements under quasi-uniaxial pressure and observed a sluggish IMT at 35 GPa accompanied by a structure change. This work did not observe superconductivity down to 2 K in contrast to FePSe₃ (max T_c ~ 5.5 K at 30 GPa)⁴. The observed structure evolution differs from earlier reports that applied a different pressure media.³ It is suggested that the phase stability fields of NiPS₃ are highly dependent on the stress state.

[1] Wildes et al., Phys. Rev. B 92, 224408 (2015).

[2] H.S. Kim et al., Phys. Rev. Lett. 123, 236401 (2019).

[3] X. Ma et al., Sci. China Physics, Mech. Astron. 64, 297011 (2021).

[4] Y. Wang et al. Nature Communications 9, 1914 (2018)