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

Jimin Zhao

Institute of Physics, Chinese Academy of Sciences, Beijing China

We report a time-resolved ultrafast quasiparticle dynamics investigation of cubic boron arsenide (c-BAs), which is a recently discovered highly thermal 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 [1]. Significantly, the EPC strength is obtained from the dynamics, with a value of  λ = 0.008, demonstrating an unusually weak coupling between the electrons and phonons. As a comparison, an ultraweak EPC strength for graphene is also expected. 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.

Time permits, I will also talk about two other recent progresses: (1) We have conceived and constructed an on-site in situ high-pressure ultrafast pump-probe spectroscopy instrument that facilitates ultrafast pump-probe dynamics measurements under high pressure condition [2]. (2) We demonstrate that second harmonic generation (SHG) is a local microscopic process—it does not rely on macroscopic broken inversion symmetry [3]. An AB-type superstructure can generate SHG easily and an ABC-type super-structure is not necessary. Our results introduce a scheme for SHG, extending the generation and control of SHG in nano-photonics to nearly all the accessible centrosymmetric materials.

1. Z. Y. Tian, Y. W. Xiao, Q. Y. Zhang, G. A. Gamage, F. Tian, S. Yue, V. G. Hadjiev, Jiming Bao, Zhifeng Ren, Erjun Liang,† and Jimin Zhao*, Ultraweak electron-phonon coupling strength in cubic boron arsenide unveiled by ultrafast dynamics, Submitted (2021).
2. Y. L. Wu, X. Yin, J. Z. L. Hasaien, Z. Y. Tian, Yang Ding, and Jimin Zhao*, On-site in situ high-pressure ultrafast pump-probe spectroscopy instrument, Rev. of Sci. Instrum. 92, 113002 (2021).
3. Hui Zhao, Qichang An, X. Ye, B. H. Yu, Q. H. Zhang, F. Sun, Q. Y. Zhang, Fang Yang, Jiandong Guo*, and Jimin Zhao*, Second harmonic generation in AB-type LaTiO3/SrTiO3 superlattices, Nano Energy 82, 105752 (2021).

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