# Dynamic conductivity in graphene beyond linear response

## TL;DR

This paper investigates the nonlinear regime of dynamic conductivity in graphene, revealing that strong electric fields induce Rabi oscillations, leading to current saturation and increased optical transparency, extending understanding beyond linear response theory.

## Contribution

It introduces a theoretical framework for ac conductivity in graphene beyond linear response, highlighting Rabi oscillations and nonlinear effects on optical transparency.

## Key findings

- Current saturates at high electric fields due to Rabi oscillations.
- Optical transparency of graphene increases with nonlinear effects.
- Nonlinear response predictions align with potential experimental observations.

## Abstract

The independence of the dynamic conductivity of intrinsic graphene of frequency takes its origin in the compensation of the vanishing density of states by the diverging matrix element of the corresponding interband transition. The applicability of the linear response approach, however, breaks down when this matrix element becomes comparable with the inverse electron lifetime. We show that the physics of the ac conductivity in this regime is determined by Rabi oscillations and obtain it beyond the first order perturbation theory. Under strong applied electric fields the induced current eventually saturates at a value determined by the frequency and the lifetime. We also calculate the electromagnetic response of a graphene sheet and find that the optical transparency is increased by the non-linear effects and make experimental predictions.