Observation of suppressed terahertz absorption in photoexcited graphene

TL;DR

This study reveals that photoexcited graphene exhibits suppressed terahertz absorption, contrasting typical semiconductors, with non-Drude spectral behavior indicating unique non-equilibrium optical properties.

Contribution

It demonstrates the counterintuitive suppression of THz absorption in photoexcited graphene and explores its non-Drude spectral characteristics, advancing understanding of graphene's optical response.

Findings

Reduced THz absorption in photoexcited graphene

Non-Drude spectral shape observed

Discussion of mechanisms behind low-frequency response

Abstract

When light is absorbed by a semiconductor, photoexcited charge carriers enhance the absorption of far-infrared radiation due to intraband transitions. We observe the opposite behavior in monolayer graphene, a zero-gap semiconductor with linear dispersion. By using time domain terahertz (THz) spectroscopy in conjunction with optical pump excitation, we observe a reduced absorption of THz radiation in photoexcited graphene. The measured spectral shape of the differential optical conductivity exhibits non-Drude behavior. We discuss several possible mechanisms that contribute to the observed low-frequency non-equilibrium optical response of graphene.