Dirac excited state quenching in graphene

TL;DR

This study introduces a novel method to measure hot carrier dynamics in graphene, revealing ultrafast cooling and efficient quenching of Dirac fermions, advancing understanding of relativistic plasma states.

Contribution

We demonstrate a sensitive thermometry technique for hot Dirac fermions in graphene, uncovering ultrafast cooling rates and enhanced quenching mechanisms in high-mobility heterostructures.

Findings

Electronic temperature quenched at 50 K

Cooling rate exceeds 10^14 K/s within 1 ps

Enhanced quenching with in-plane voltages

Abstract

Hot, dense phases of Dirac fermions - predicted to resemble relativistic plasma - are uniquely accessible through photoexcitation of pristine, charge neutral graphene. We demonstrate a sensitive temperature probe of the photoexcited Dirac state, called interlayer optoelectronic thermometry, which measures out-of-plane transport of hot carriers in high-mobility, neutral graphene encapsulated within graphene-hBN-graphene heterostructures. At a critical intermediate sample temperature T = 50 K, the electronic temperature Te is quenched, exhibiting an intrinsic cooling rate that exceeds 10^14 Kelvin/s within the first picosecond after photoexcitation. Quenching is further enhanced by applying in-plane voltages within the stack-engineered heterostructure. Extreme sensitivity of Te to sample temperature and applied voltages reveals anomalously efficient hot-carrier quenching, which we identify as an essential feature of the strongly interacting hot Dirac excited state.