Universal behavior at discontinuous quantum phase transitions

TL;DR

This paper explores the mechanisms behind the change from second to first order in quantum phase transitions, focusing on coupling to soft modes and competing orders, with implications for heavy fermion systems.

Contribution

It provides a theoretical analysis of mechanisms causing discontinuous quantum phase transitions and describes thermodynamic behavior near these transitions in heavy fermion materials.

Findings

Coupling to soft modes can induce first order transitions.

Competition between different orders influences transition nature.

Thermodynamic behavior near first order quantum transitions is characterized.

Abstract

Discontinuous quantum phase transitions besides their general interest are clearly relevant to the study of heavy fermions and magnetic transition metal compounds. Recent results show that in many systems belonging to these classes of materials, the magnetic transition changes from second order to first order as they approach the quantum critical point (QCP). We investigate here some mechanisms that may be responsible for this change. Specifically the coupling of the order parameter to soft modes and the competition between different types of order near the QCP. For weak first order quantum phase transitions general results are obtained. In particular we describe the thermodynamic behavior at this transition when it is approached from finite temperatures. This is the discontinuous equivalent of the non-Fermi liquid trajectory close to a conventional QCP in a heavy fermion material.