Hot electron cooling by acoustic phonons in graphene

TL;DR

This study investigates hot electron cooling in graphene, revealing a T4 dependence of cooling power due to acoustic phonons and highlighting the impact of lattice disorder on electron-phonon coupling.

Contribution

It provides experimental evidence of acoustic phonon cooling in graphene and quantifies the electron-phonon coupling constant, considering effects of lattice disorder.

Findings

Cooling power follows a T4 dependence at high bias.

Lattice disorder reduces the electron-phonon coupling constant.

Supports development of graphene-based bolometric detectors.

Abstract

We have investigated the energy loss of hot electrons in metallic graphene by means of GHz noise thermometry at liquid helium temperature. We observe the electronic temperature T / V at low bias in agreement with the heat diffusion to the leads described by the Wiedemann-Franz law. We report on $T\propto\sqrt{V}$ behavior at high bias, which corresponds to a T4 dependence of the cooling power. This is the signature of a 2D acoustic phonon cooling mechanism. From a heat equation analysis of the two regimes we extract accurate values of the electron-acoustic phonon coupling constant $\Sigma$ in monolayer graphene. Our measurements point to an important effect of lattice disorder in the reduction of $\Sigma$, not yet considered by theory. Moreover, our study provides a strong and firm support to the rising field of graphene bolometric detectors.