Anharmonicity in one-dimensional electron-phonon system

TL;DR

This study explores how anharmonicity influences phase transitions in a one-dimensional electron-phonon system, revealing that anharmonicity suppresses dimerization and charge density waves, with implications for understanding quantum phase behavior.

Contribution

It provides the first detailed quantum Monte Carlo analysis of anharmonic effects on phase transitions in the 1D Holstein model, highlighting the role of anharmonicity in phase stability.

Findings

Anharmonicity suppresses dimerization and charge density waves.

A phase transition from disorder to dimerized phase occurs with and without anharmonicity.

Disorder phase exhibits metallic behavior with gapless charge excitations.

Abstract

We investigate the effect of anharmonicity on the one-dimensional half-filled Holstein model by using the determinant quantum Monte Carlo method. By calculating the order parameters we find that with and without anharmonicity there is always an transition from a disorder phase to a dimerized phase. Moreover, in the dimerized phase a lattice dimerization and a charge density wave coexist. The anharmonicity represented by the quartic term suppresses the dimerization as well as the charge density wave, while a double-well potential favors the dimerization. In addition, by calculating the correlation exponents we show that the disorder phase is metallic with gapless charge excitations and gapful spin excitations while in the dimerized phase both excitations are gapful.