Quasiparticle dynamics and electron-phonon coupling in Weyl semimetal TaAs

Abstract

We report ultrafast quasiparticle (QP) dynamics of TaAs, from which we obtain its electron-phonon coupling (EPC) strength. Two relaxation components with lifetimes ${\ensuremath{\tau}}_{\mathrm{fast}}=0.48\phantom{\rule{0.16em}{0ex}}\mathrm{ps}$ and ${\ensuremath{\tau}}_{\mathrm{slow}}=250\phantom{\rule{0.16em}{0ex}}\mathrm{ps}$ are observed, each of which exhibits a smooth temperature dependence. Furthermore, we carry out a fluence-dependence investigation, based on which the quantitative analysis of the fast relaxation component yields a constant EPC strength \ensuremath{\lambda} with $\ensuremath{\lambda}\ensuremath{\langle}{\mathrm{\ensuremath{\Omega}}}^{3}\ensuremath{\rangle}/{\ensuremath{\langle}\mathrm{\ensuremath{\Omega}}\ensuremath{\rangle}}^{2}\ensuremath{\approx}5.2\phantom{\rule{0.16em}{0ex}}\mathrm{p}{\mathrm{s}}^{\ensuremath{-}1}$. In addition, our rotational polarization angle experiment demonstrates that the QP ultrafast dynamics is nearly isotropic under the given excitation geometry. Our investigation of the EPC strength accounts for the so far relatively rarely explored medium fluence regime, which can be generalized to various types of quantum materials.