Low-energy instability of flexural phonons in graphene

TL;DR

This paper investigates how electron interactions influence flexural phonons in graphene, revealing two phases with distinct renormalization behaviors of bending rigidity, and highlighting potential for phonon condensate formation.

Contribution

It introduces a combined self-consistent and renormalization group approach to analyze electron-induced phonon instability in graphene, identifying two distinct phases.

Findings

Identification of two phases with different rigidity renormalization behaviors

Softening of phonon dispersion at intermediate scales

Potential for flexural phonon condensate formation

Abstract

We study the effect exerted by the electrons on the flexural phonons in graphene, accounting for the attractive interaction created by the exchange of electron-hole excitations. Combining the self-consistent computation of the phonon self-energy with renormalization group methods, we show that graphene has two different phases corresponding to soft and strong renormalization of the bending rigidity in the long-wavelength limit. In the first case, the system may have an intermediate scale in which the phonon dispersion is softened, but it manages finally to become increasingly rigid over large distance scales. The strongly renormalized phase is closer however to critical behavior, with an effective rigidity that becomes pinned in practice at very small values, implying a very large susceptibility for the development of a condensate of the flexural phonon field.