Ultraweak Electron-Phonon Coupling Strength in Cubic Boron Arsenide Unveiled by Ultrafast Dynamics

We report a time-resolved ultrafast quasiparticle dynamics investigation of c-BAs, which is a recently discovered highly thermally conducting material. The excited-state ultrafast relaxation channels dictated by the electron-phonon coupling (EPC), phonon-phonon scattering, and radiative electron-hole recombination have been unambiguously identified, along with their typical interaction times. Significantly, the EPC strength is obtained from the dynamics, with a value of <i>λ</i>_T₂= 0.008 (corresponding to λ&lt;Ω²&gt; = 1.18 ± 0.08 ps^–2), demonstrating an unusually weak coupling between the electrons and phonons. As a comparison, an ultraweak EPC strength for graphene is also expected. We propose that preserving an ultrasmall EPC strength may be a prerequisite for exhibiting an ultrahigh thermal conductivity. Our investigation provides insight for searching and designing ultrahigh thermal conductivity materials. Notably, during our analysis we have generalized the fluence-dependence method for obtaining the EPC strength to room temperature, which can be applied to many other types of quantum materials in the future.