Magnetism, structure, and charge correlation at a pressure-induced Mott-Hubbard insulator-metal transition

TL;DR

This study investigates how pressure influences the magnetic, structural, and electronic properties of NiS2 during its transition from an insulator to a metal, revealing complex charge and magnetic interactions.

Contribution

It provides new insights into the pressure-induced Mott-Hubbard transition, highlighting the role of charge correlations and structural symmetry changes in NiS2.

Findings

Pressure suppresses insulating state while enhancing magnetism.

Lattice symmetry reduces from cubic to monoclinic in the metallic phase.

Phase separation occurs over a wide pressure range.

Abstract

We use synchrotron x-ray diffraction and electrical transport under pressure to probe both the magnetism and the structure of single crystal NiS2 across its Mott-Hubbard transition. In the insulator, the low-temperature antiferromagnetic order results from superexchange among correlated electrons and couples to a (1/2, 1/2, 1/2) superlattice distortion. Applying pressure suppresses the insulating state, but enhances the magnetism as the superexchange increases with decreasing lattice constant. By comparing our results under pressure to previous studies of doped crystals we show that this dependence of the magnetism on the lattice constant is consistent for both band broadening and band filling. In the high pressure metallic phase the lattice symmetry is reduced from cubic to monoclinic, pointing to the primary influence of charge correlations at the transition. There exists a wide regime of phase separation that may be a general characteristic of correlated quantum matter.