Breaking Pauli blockade via ultrafast cooling of hot electrons in optically-pumped graphene

TL;DR

This study demonstrates that ultrafast cooling of hot electrons in optically-pumped graphene can break the Pauli blockade, resulting in enhanced optical absorption, revealing new insights into ultrafast carrier dynamics in 2D materials.

Contribution

First direct observation showing that ultrafast hot electron cooling in graphene breaks Pauli blockade, influencing nonlinear optical properties and device design.

Findings

Pauli blockade is broken by ultrafast hot electron cooling.

Electron excitation and decay occur on similar femtosecond timescales.

Enhanced optical absorption results from blockade breaking.

Abstract

Pauli blockade occurs when the excited electrons fill up the states near the conduction bands and block subsequent absorption in semiconductors, and has been widely applied in mode-locking for passively-pulsed-laser systems. In this letter, we report the first direct observation that the Pauli blockade is broken by ultrafast cooling of hot electrons in optically-pumped graphene. With femtosecond spectroscopy, we demonstrate that the time scale to excite an electron (~100 fs) is of the same order as that of the electron decay via electron-electron scattering, which allows the electron excitation interplays strongly with the cooling of hot electrons. Consequently, Pauli blockade is dismissed, leading to an unconventionally enhanced optical absorption. We suggest that this effect is a universal feature of two-dimensional layered materials, which sheds the light of ultrafast carrier dynamics in nonlinear physics and inspires the designing of new-generation of ultrafast optoelectronic devices.