Strain-tunable metamagnetic critical endpoint in Mott insulating rare-earth titanates

TL;DR

This study reveals how uniaxial strain can tune the magnetic phase transitions in rare-earth titanates, leading to a quantum critical endpoint in an insulating Mott system, with implications for understanding complex magnetic phase diagrams.

Contribution

It demonstrates that uniaxial strain can control the metamagnetic transition and induce a quantum critical point in rare-earth titanates, expanding the understanding of magnetic phase tuning in Mott insulators.

Findings

A first-order metamagnetic transition line exists with a critical endpoint.

Uniaxial strain can tune the transition to zero temperature, creating a quantum critical point.

Octahedral rotations influence magnetic order and phase diagram topology.

Abstract

Rare-earth titanates are Mott insulators whose magnetic ground state -- antiferromagnetic (AFM) or ferromagnetic (FM) -- can be tuned by the radius of the rare-earth element. Here, we combine phenomenology and first-principles calculations to shed light on the generic magnetic phase diagram of a chemically substituted titanate on the rare-earth site that interpolates between an AFM and a FM state. Octahedral rotations present in these perovskites cause the AFM order to acquire a small FM component -- and vice-versa -- removing any multicritical point from the phase diagram. However, for a wide parameter range, a first-order metamagnetic transition line terminating at a critical endpoint survives inside the magnetically ordered phase. Like the liquid-gas transition, a Widom line emerges from the endpoint, characterized by enhanced fluctuations. In contrast to metallic FMs, this metamagnetic transition involves two symmetry-equivalent and insulating canted spin states. Moreover, instead of a magnetic field, we show that uniaxial strain can be used to tune this transition to zero temperature, inducing a quantum critical endpoint.