Quantum triple point and quantum critical endpoints in metallic magnets

TL;DR

This paper explores how quantum fluctuations fundamentally change the phase diagrams of metallic magnets, leading to phenomena like quantum triple points and critical endpoints that are absent in classical models.

Contribution

It introduces the concept of quantum triple points and quantum critical endpoints in metallic magnets, revealing new phase transition behaviors driven by quantum fluctuations.

Findings

Quantum fluctuations shrink the coexistence region of FM and AFM phases.

Transitions can change from second to first order due to quantum effects.

Magnetic fields can induce quantum triple points and critical endpoints.

Abstract

In low-temperature metallic magnets, ferromagnetic (FM) and antiferromagnetic (AFM) orders can exist in a single system in different parts of the phase diagram as a function of some control parameter. These phases can be adjacent, or exist concurrently, resulting in a phase transition between a FM phase and an AFM one, or between a phase of concurrent FM and AFM order and either of the pure phases. We show that universal quantum fluctuations qualitatively alter the known phase diagrams for classical magnets: They shrink the region of concurrent FM and AFM order, change various transitions from second to first order, and, in the presence of a magnetic field, lead to either a quantum triple point where the FM, AFM and paramagnetic phases coexist, or to a quantum critical end point.