Polaronic and nonadiabatic phase diagram from anomalous isotope effects

TL;DR

This paper explores how isotope effects reveal the influence of lattice dynamics on physical properties in the Holstein model, highlighting nonadiabatic effects and identifying a new crossover with large isotope anomalies.

Contribution

It introduces a nonadiabatic phase diagram showing a novel crossover point with significant isotope effects, expanding understanding of lattice fluctuation impacts.

Findings

Isotope coefficients are large even away from polaronic crossover.

Nonadiabatic lattice fluctuations are crucial in weak to moderate coupling.

A new crossover with maximal isotope effects is identified.

Abstract

Isotope effects (IEs) are powerful tool to probe directly the dependence of many physical properties on the lattice dynamics. In this paper we invenstigate the onset of anomalous IEs in the spinless Holstein model by employing the dynamical mean field theory. We show that the isotope coefficients of the electron effective mass and of the dressed phonon frequency are sizeable also far away from the strong coupling polaronic crossover and mark the importance of nonadiabatic lattice fluctuations in the weak to moderate coupling region. We characterize the polaronic regime by the appearence of huge IEs. We draw a nonadiabatic phase diagram in which we identify a novel crossover, not related to polaronic features, where the IEs attain their largest anomalies.