Strongly-coupled quantum critical point in an all-in-all-out antiferromagnet

TL;DR

This study uncovers a quantum critical point in Cd2Os2O7 where magnetic order and lattice structure change continuously under high pressure, revealing strongly-coupled quantum criticality in a 3D system.

Contribution

It reports the discovery of a quantum critical point in an all-in-all-out antiferromagnet using advanced high-pressure x-ray techniques, highlighting strongly-coupled quantum critical behavior.

Findings

Quantum critical point where magnetic order vanishes

Continuous change in lattice structure from Fd-3m to F-43m

Presence of strongly-coupled spin, lattice, and quasiparticle excitations

Abstract

Dimensionality and symmetry play deterministic roles in the laws of Nature. They are important tools to characterize and understand quantum phase transitions, especially in the limit of strong correlations between spin, orbit, charge, and structural degrees of freedom. Using newly-developed, high-pressure resonant x-ray magnetic and charge diffraction techniques, we have discovered a quantum critical point in Cd2Os2O7 as the all-in-all-out (AIAO) antiferromagnetic order is continuously suppressed to zero temperature and, concomitantly, the cubic lattice structure continuously changes from space group Fd-3m to F-43m. Surrounded by three phases of different time reversal and spatial inversion symmetries, the quantum critical region anchors two phase lines of opposite curvature, with striking departures from a mean-field form at high pressure. As spin fluctuations, lattice breathing modes, and quasiparticle excitations interact in the quantum critical region, we argue that they present the necessary components for strongly-coupled quantum criticality in this three-dimensional compound.