Thermodynamic picture of ultrafast charge transport in graphene.

Zoltán Mics,Khaled Parvez,Klaus Müllen,Søren A Jensen,Mischa Bonn,Ivan Ivanov,Dmitry Turchinovich,Xinliang Feng,Klaas-Jan Tielrooij

doi:10.1038/ncomms8655

Abstract

The outstanding charge transport properties of graphene enable numerous electronic applications of this remarkable material, many of which are expected to operate at ultrahigh speeds. In the regime of ultrafast, sub-picosecond electric fields, however, the very high conduction properties of graphene are not necessarily preserved, with the physical picture explaining this behaviour remaining unclear. Here we show that in graphene, the charge transport on an ultrafast timescale is determined by a simple thermodynamic balance maintained within the graphene electronic system acting as a thermalized electron gas. The energy of ultrafast electric fields applied to graphene is converted into the thermal energy of its entire charge carrier population, near-instantaneously raising the electronic temperature. The dynamic interplay between heating and cooling of the electron gas ultimately defines the ultrafast conductivity of graphene, which in a highly nonlinear manner depends on the dynamics and the strength of the applied electric fields.

Highlights

The outstanding charge transport properties of graphene enable numerous electronic applications of this remarkable material, many of which are expected to operate at ultrahigh speeds
We present a unifying view on electron transport in graphene in arbitrary ultrafast electric fields
We demonstrate that the conductivity of graphene in a very wide range of applied electric field strengths and frequencies can be described within a simple thermodynamic approach: by taking into account the statistically determined thermal balance maintained within the entire electron population of graphene interacting with the applied electric field, and without requiring detailed knowledge of the microscopic electron kinetics

Summary

Introduction

The outstanding charge transport properties of graphene enable numerous electronic applications of this remarkable material, many of which are expected to operate at ultrahigh speeds. In the regime of ultrafast, sub-picosecond electric fields, the very high conduction properties of graphene are not necessarily preserved, with the physical picture explaining this behaviour remaining unclear. We show that in graphene, the charge transport on an ultrafast timescale is determined by a simple thermodynamic balance maintained within the graphene electronic system acting as a thermalized electron gas. The exceptional conductive properties of graphene are not necessarily maintained in the regime where the applied electric field oscillates at very high, THz rates corresponding to picosecond or sub-picosecond duration of field cycles. We demonstrate that the conductivity of graphene in a very wide range of applied electric field strengths and frequencies can be described within a simple thermodynamic approach: by taking into account the statistically determined thermal balance maintained within the entire electron population of graphene interacting with the applied electric field, and without requiring detailed knowledge of the microscopic electron kinetics

Methods

Results

Conclusion