Abstract
Femtosecond spectroscopy is applied to study transient electronic processes in bismuth. The components with relaxation times of 1 ps, 7 ps, and ∼1 ns are detected in the photoinduced reflectivity response of the crystal. To facilitate assignment of the observed relaxation to the decay of particular excited electronic states, we use pump pulses with central wavelengths ranging from 400 to 2300 nm. Additionally, we examine the variation of parameters of coherent A1g phonons upon the change of excitation and probing conditions. Data analysis reveals significant wavevector dependence of electron-hole and electron-phonon coupling strength along Γ-T direction of the Brillouin zone.
Highlights
Bismuth is a semimetal with unique electronic properties, which are to the large extent governed by symmetry considerations inherent for Peierls-distorted crystals
If decay rates of nonequilibrium electrons were addressed, both the reported values and the interpretation vary from paper to paper
Detailed knowledge of ultrafast electronic dynamics of bismuth is necessary for a number of theoretical and practical questions
Summary
Bismuth is a semimetal with unique electronic properties, which are to the large extent governed by symmetry considerations inherent for Peierls-distorted crystals. Unlike many other elemental crystals, ultrafast electronic dynamics in bismuth attracted less attention than it deserves. Femtosecond optical pump-probe experiments performed with bismuth so far generally focused upon detection of coherent phonons, treating electronic response only as a background. If decay rates of nonequilibrium electrons were addressed, both the reported values and the interpretation vary from paper to paper. Detailed knowledge of ultrafast electronic dynamics of bismuth is necessary for a number of theoretical and practical questions. First of all it is needed for a deeper understanding of transient structural phenomena: coherent phonons [1] and ultrafast disordering [2]. Thereby it was possible to evaluate electron-hole recombination and electron-phonon coupling rates for certain regions of the Brillouin zone
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