Ultrafast Band-Gap Renormalization in Bilayer Graphene

TL;DR

This study uses femtosecond spectroscopy to demonstrate ultrafast, reversible control of bilayer graphene's electronic band structure through photoinduced charge transfer and hot-carrier effects, enabling potential ultrafast optoelectronic applications.

Contribution

It reveals two mechanisms—interlayer charge transfer and hot-carrier screening—that enable ultrafast, reversible band-gap modulation in bilayer graphene, advancing control over its electronic properties.

Findings

Transient band-gap opening on femtosecond timescales

Hot-carrier population enhances electronic screening

Reversible control of electronic band structure

Abstract

We demonstrate, by femtosecond time- and angle-resolved photoemission spectroscopy, that photoinduced interlayer charge transfer in a heterostructure consisting of Bernal-stacked bilayer graphene and a single atomic layer of silver on 6H-SiC(0001) transiently modulates the intrinsic potential landscape across the silver-graphene interface. This acts as an ultrafast optoelectronic gate that drives momentum-dependent band renormalizations, resulting in a transient band-gap opening on femtosecond timescales. Simultaneously, the photogenerated hot-carrier population enhances electronic screening, leading to subsequent closing of the band-gap beyond the thermal equilibrium value. These findings reveal two different mechanisms for photoinduced, reversible control of the electronic band structure in bilayer graphene -- interlayer charge transfer and hot-carrier-enhanced screening -- providing a general framework for the ultrafast control of electronic properties in graphene-based heterostructures. This opens up novel pathways for the realization of ultrafast optoelectronic devices and the exploration of correlated quantum phases in bilayer graphene under non-equilibrium conditions.