Quantum phase transitions in electronic systems

TL;DR

This review explains quantum phase transitions in electronic systems, highlighting their unique quantum-driven nature, examples like ferromagnetic and antiferromagnetic transitions, and effects of disorder and interactions on these phenomena.

Contribution

It provides a comprehensive pedagogical overview of quantum phase transitions in electronic systems, emphasizing recent theoretical insights and complex behaviors due to disorder and electron interactions.

Findings

Ferromagnetic transition exhibits long-range interactions due to electronic soft modes.

Rare regions significantly influence quantum phase transitions in disordered systems.

Disorder and interactions critically affect metal-insulator transitions.

Abstract

Quantum phase transitions occur at zero temperature when some non-thermal control-parameter like pressure or chemical composition is changed. They are driven by quantum rather than thermal fluctuations. In this review we first give a pedagogical introduction to quantum phase transitions and quantum critical behavior emphasizing similarities with and differences to classical thermal phase transitions. We then illustrate the general concepts by discussing a few examples of quantum phase transitions occurring in electronic systems. The ferromagnetic transition of itinerant electrons shows a very rich behavior since the magnetization couples to additional electronic soft modes which generates an effective long-range interaction between the spin fluctuations. We then consider the influence of rare regions on quantum phase transitions in systems with quenched disorder, taking the antiferromagnetic transitions of itinerant electrons as a primary example. Finally we discuss some aspects of the metal-insulator transition in the presence of quenched disorder and interactions.