Revealing the ultrafast light-to-matter energy conversion before heat diffusion in a layered Dirac semimetal

TL;DR

This study investigates ultrafast light-to-matter energy conversion in a layered Dirac semimetal, revealing a bottleneck in electronic recovery and unconventional cooling before heat diffusion, advancing understanding of out-of-equilibrium phenomena.

Contribution

It demonstrates the applicability of the two-temperature model to layered Dirac semimetals and identifies the dynamics preceding heat diffusion, providing new insights into ultrafast energy transfer mechanisms.

Findings

Electronic recovery slows with increased pump power at ~1 ps

Unconventional power-law cooling occurs at ~100 ps

Criteria for the applicability of the two-temperature model are established

Abstract

There is still no general consensus on how one can describe the out-of-equilibrium phenomena in matter induced by an ultrashort light pulse. We investigate the pulse-induced dynamics in a layered Dirac semimetal SrMnBi2 by pump-and-probe photoemission spectroscopy. At ~<1 ps, the electronic recovery slowed upon increasing the pump power. Such a bottleneck-type slowing is expected in a two-temperature model (TTM) scheme, although opposite trends have been observed to date in graphite and in cuprates. Subsequently, an unconventional power-law cooling took place at ~100 ps, indicating that spatial heat diffusion is still ill defined at ~100 ps. We identify that the successive dynamics before the emergence of heat diffusion is a canonical realization of a TTM scheme. Criteria for the applicability of the scheme is also provided.