The phase diagram and the structure of CDW state in high magnetic field in quasi-1D materials: mean-field approach

TL;DR

This paper develops a mean-field theory for charge-density wave states in high magnetic fields in quasi-1D materials, revealing complex phase transitions, harmonic modulations, and the effects of imperfect nesting.

Contribution

It introduces a detailed mean-field model describing CDW states under magnetic fields, including the nature of phase transitions and harmonic modulations, with insights into the effects of imperfect nesting.

Findings

CDW$_x$ phase has at least double harmonic modulation in most of the phase diagram.

Transition from CDW$_0$ to CDW$_x$ is first order with a jump in order parameter and wave vector.

Imperfect nesting alters the phase diagram and transition characteristics.

Abstract

We develop the mean-field theory of a charge-density wave (CDW) state in magnetic field and study the properties of this state below the transition temperature. We show that the CDW state with shifted wave vector in high magnetic field (CDW$_x$ phase) has at least double harmonic modulation on the most part of the phase diagram. In the perfect nesting case the single harmonic CDW state with shifted wave vector exists only in a very narrow region near the tricritical point where the fluctuations are very strong. We show that the transition from CDW$_0$ to CDW$_x$ state below the critical temperature is accompanied by a jump of the CDW order parameter and of the wave vector rather than by their continuous increase. This implies a first order transition between these CDW states and explains the strong hysteresis accompanying this transition in many experiments. We examine how the phase diagram changes in the case of imperfect nesting.