Ultraweak electron-phonon coupling strength in cubic boron arsenide unveiled by ultrafast dynamics

We report a time-resolved ultrafast quasiparticle dynamics investigation of cubic boron arsenide (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 lambda(T2) = 0.008 (corresponding to lambda = 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.

Automated summary

We investigated the ultrafast quasiparticle dynamics of cubic boron arsenide and identified the interactions between electrons and phonons that contribute to its high thermal conductivity. The weak electron-phonon coupling strength and the importance of preserving this weak coupling for achieving ultrahigh thermal conductivity were demonstrated. Our findings offer insights for the search and design of materials with high thermal conductivity.