Quantum Monte Carlo study of an anharmonic Holstein model

TL;DR

This study uses quantum Monte Carlo simulations to explore how anharmonic phonon potentials influence the phases and superconducting properties of the Holstein model, revealing reduced charge density wave stability and enhanced superconductivity.

Contribution

It introduces anharmonicity into the Holstein model and analyzes its effects on phase transitions and superconductivity using quantum Monte Carlo methods.

Findings

Anharmonicity reduces the charge density wave phase and transition temperature.

A first order phase transition occurs between CDW and homogeneous phases away from half-filling.

Anharmonicity enhances the superconducting susceptibility in the doped region.

Abstract

We study the effects of anharmonicity on the physics of the Holstein model, which describes the coupling of itinerant fermions and localized quantum phonons, by introducing a quartic term in the phonon potential energy. We find that the presence of this anharmonic term reduces the extent of the charge density wave phase (CDW) at half-filling as well as the transition temperature to this phase. Doping away from half-filling, we observe a first order phase transition between the CDW and a homogeneous phase which is also present in the harmonic model. In addition, we study the evolution of the superconducting susceptibility in the doped region and show that anharmonicity can enhance the superconducting response.