Unconventional critical behaviour in a quasi-two-dimensional organic conductor

TL;DR

This study investigates the critical behavior of a pressure-induced Mott transition in a quasi-two-dimensional organic conductor, revealing unique universality class characteristics not matching known models, thus advancing understanding of electronic phase transitions.

Contribution

The paper reports the first observation of unconventional critical behavior at the Mott transition in a quasi-two-dimensional organic material, indicating a new universality class.

Findings

Critical phenomena observed differ from known universality classes.

The Mott transition exhibits unique collective behavior in two dimensions.

Results suggest new theoretical models are needed for 2D Mott transitions.

Abstract

Changing the interactions between particles in an ensemble-by varying the temperature or pressure, for example-can lead to phase transitions whose critical behaviour depends on the collective nature of the many-body system. Despite the diversity of ingredients, which include atoms, molecules, electrons and their spins, the collective behaviour can be grouped into several families (called 'universality classes') represented by canonical spin models1. One kind of transition, the Mott transition2, occurs when the repulsive Coulomb interaction between electrons is increased, causing wave-like electrons to behave as particles. In two dimensions, the attractive behaviour responsible for the superconductivity in high-transition temperature copper oxide3,4 and organic5-7 compounds appears near the Mott transition, but the universality class to which two-dimensional, repulsive electronic systems belongs remains unknown. Here we present an observation of the critical phenomena at the pressure-induced Mott transition in a quasi-two-dimensional organic conductor using conductance measurements as a probe. We find that the Mott transition in two dimensions is not consistent with known universality classes, as the observed collective behaviour has previously not been seen. This peculiarity must be involved in any emergent behaviour near the Mott transition in two dimensions.