Layered materials, thermal transport

In this talk, I will present three very recent results from my group, related to thermal transport in layered materials. The first topic pertains to phonon heat transport in suspended transition metal dichalcogenide films from bulk down to the monolayer. We prepared these systems using exfoliation and dry transfer [1], performed measurements using Raman thermometry, where we identified and eliminated several important artefacts, and compared the experimental results with our theoretical results based on ab-initio simulations, that are valid at finite temperature, rather than 0 K [2]. For the second topic, we developed an ultrafast spatiotemporal photocurrent technique that allows us to follow electronic heat spreading in time and space. We applied this technique to graphene, where we found a giant diffusivity when tuning to the quantum-critical Dirac-fluid regime, with heat spreading over microns in a timescale of a few hundred femtoseconds [3]. For the final topic, we developed an ultrafast spatiotemporal setup for following phonon heat spreading in suspended films. This technique gives quantitative access to the in-plane diffusivity of suspended thin films, without the need for any material input parameters, while requiring heating of only a few Kelvin [4]. [1] S. Varghese et al. J. Phys. Mater. 4, 046001 (2021) [2] D. Saleta et al. under review [3] A. Block et al. Nat. Nanotechnol. (2021), published online [4] S. Varghese et al. in preparation