Unveiling the Unusual Electron–Phonon Interaction and Quasi-Particle Dynamics in type-II Weyl Semimetal NbIrTe4

Layered ternary type-II Weyl semimetals demonstrate promising applications in high-performance and broadband optoelectronics, therefore it is crucial to gain insights into their photocarriers’ dynamics. In this work, the probing polarization dependence of non-equilibrium dynamics in NbIrTe₄ is investigated by using transient reflectivity spectroscopy. Following photoexcitation at 3.18 eV, the dynamical response of 1.59 eV probe pulse exhibits a strong dependence on probe polarization. The relaxation comprises two components: a rapid recovery of ≈0.6 ps attributed to the electron–phonon scattering, and an anomalous slow recovery spanning hundreds of picoseconds attributed to the photoinduced quasi-particle. The polarization dependence of rapid relaxation time τ is indicative of the in-plane anisotropy of electron–phonon coupling in NbIrTe₄. The slow relaxation modulated by a latest reported 16 cm⁻¹ coherent phonon also shows strong probing polarization dependence, further revealing the anisotropic nature of electron–phonon coupling and the possibility of anisotropic lattice distortion, as well as photoinduced polaron, under ultrafast photoexcitation in NbIrTe₄. The dynamical anisotropy in NbIrTe₄ has provided valuable guidance for the application of NbIrTe₄ in polarization-sensitive nonlinear optics or optoelectronic devices and offers insights into the unique carrier transport as well as phonon transport properties of this newly established topological material.