Ultrafast heat dynamics and transport in (twisted) quantum materials

Speaker: Klaas-Jan Tielrooij – Eindhoven Universitiy of Technology

Host: Hai Wang

Abstract:

When light is absorbed by graphene, several interesting ultrafast thermodynamic phenomena occur. These phenomena are moreover useful for applications, such as ultrafast photodetectors. The ultrafast thermodynamic phenomena typically involve electron thermalization through electron-electron interactions on a 10-100 fs timescale, followed by electron cooling by emission of phonons or by diffusion of electronic heat. In this talk, I will show two recent results related to the ultrafast thermodynamics in (twisted bilayer) graphene. The first result [1] is that the electron cooling dynamics in twisted bilayer graphene near the magic angle (1.1°) is very distinct from the dynamics in monolayer or non-twisted bilayer graphene. Specifically, the cooling time in near-magic twisted bilayer graphene is a few picoseconds all the way from room temperature down to 10 K. We ascribe this to a novel physical phenomenon: Umklapp-assisted electron-phonon cooling, facilitated by the moiré pattern in twisted bilayer graphene. The second result [2] is that the diffusion of electronic heat in graphene in the hydrodynamic regime can be exceptionally fast, as measured through spatiotemporal thermoelectric microscopy. Specifically, in the Dirac fluid regime, close to the Dirac point, we discovered a short-lived (few 100 fs) thermal conductivity that exceeds 10,000 W/m/K – even larger than the record-high thermal conductivity of phonons. Finally, if time permits, I will make an attempt at answering the following question: Can 2D semiconductors compete with silicon?

REFERENCES
[1] Mehew, J.D. et al. Sci. Adv. 10, adj1361 (2024)
[2] Block, A., et al., Nat. Nanotechnol. 16, 1195-1200 (2021)