Similar ultrafast dynamics of several dissimilar Dirac and Weyl semimetals

TL;DR

This study investigates the ultrafast electron dynamics in four different Dirac and Weyl semimetals, revealing rapid relaxation processes that highlight their potential for optoelectronic applications like switches and detectors.

Contribution

It provides the first comparative ultrafast dynamics measurements across chemically and structurally diverse Dirac and Weyl semimetals, revealing common relaxation behaviors.

Findings

All materials relax within a few picoseconds after photoexcitation.

Rapid relaxation indicates potential for ultrafast optoelectronic devices.

Photoexcited carriers persist for several picoseconds, affecting optical properties.

Abstract

Recent years have seen the rapid discovery of solids whose low-energy electrons have a massless, linear dispersion, such as Weyl, line-node, and Dirac semimetals. The remarkable optical properties predicted in these materials show their versatile potential for optoelectronic uses. However, little is known of their response in the picoseconds after absorbing a photon. Here we measure the ultrafast dynamics of four materials that share non-trivial band structure topology but that differ chemically, structurally, and in their low-energy band structures: ZrSiS, which hosts a Dirac line node and Dirac points; TaAs and NbP, which are Weyl semimetals; and Sr$_{1-y}$Mn$_{1-z}$Sb$_2$, in which Dirac fermions coexist with broken time-reversal symmetry. After photoexcitation by a short pulse, all four relax in two stages, first sub-picosecond, and then few-picosecond. Their rapid relaxation suggests that these and related materials may be suited for optical switches and fast infrared detectors. The complex change of refractive index shows that photoexcited carrier populations persist for a few picoseconds.