# Inverse pressure-induced Mott transition in TiPO$_4$

## TL;DR

This study uses ab-initio calculations to explore pressure-induced electronic and magnetic phase transitions in TiPO$_4$, revealing a collapse and reemergence of Mott insulating behavior and magnetism under high pressure.

## Contribution

It provides the first detailed theoretical analysis of the structural and electronic transitions in TiPO$_4$ under high pressure, including the novel phase V with 5-fold O-coordinated P-atoms.

## Key findings

- Collapse of the Mott gap at phase transition
- Reappearance of Mott insulating phase V with antiferromagnetism
- Pressure-induced quenching and recovery of magnetic properties

## Abstract

TiPO$_4$ shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high pressure experiments for TiPO$_4$ reported two new structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053]. The latter was shown to include the first example of 5-fold O-coordinated P-atoms in an inorganic phosphate compound. In this work we characterize the electronic structure and other physical properties of these new phases by means of ab-initio calculations, and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments.