Ultrafast Hot-Carrier cooling in Quasi Freestanding Bilayer Graphene with Hydrogen Intercalated Atoms

TL;DR

This study investigates hot-carrier cooling in bilayer graphene with hydrogen intercalation, revealing longer relaxation times due to substrate decoupling and identifying electron-optical phonon scattering as the main cooling mechanism.

Contribution

It provides new insights into hot-carrier cooling dynamics in quasi-freestanding bilayer graphene and clarifies the dominant relaxation process.

Findings

Longer decay times (2.6 to 6.4 ps) compared to monolayer graphene.

Cooling times increase nonlinearly with excitation intensity.

Cooling primarily via electron-optical phonon scattering, not supercollision mechanism.

Abstract

We perform a femtosecond-THz optical pump-probe spectroscopy to investigate the cooling dynamics of hot carriers in quasi-free standing bilayer epitaxial graphene. We observed longer decay time constants, in the range of 2.6 to 6.4 ps, compared to previous studies on monolayer graphene, which increase nonlinearly with excitation intensity. The increased relaxation times are due to the decoupling of the graphene layer from the SiC substrate after hydrogen intercalation which increases the distance between graphene and substrate. Furthermore, our measurements do not show that the supercollision mechanism is related to the cooling process of the hot carriers, which is ultimately achieved by electron-optical phonon scattering.