Kavli Affiliate: Peidong Yang
| First 5 Authors: Jonah R. Adelman, Hugo Laurell, Lorenz Drescher, Han K. D. Le, Peidong Yang
| Summary:
The narrow bandgap semiconductor elemental tellurium (Te) has a unique
electronic structure due to strong spin-orbit splitting and a lack of inversion
symmetry of its helical lattice. Using broadband extreme ultraviolet core-level
transient absorption, we measure simultaneously the coherently coupled
photo-induced carrier and lattice dynamics at the Te N$_{4,5}$ edge initiated
by a few-cycle NIR pulse. Ultrafast excitation of carriers leads to a
coherently excited A$_{rm{1g}}$ phonon oscillation and the generation of a hot
carrier population distribution that oscillates in temperature, and the phonon
excursion and hot carrier temperature are $pi$ out of phase with respect to
each other. The depths of modulation suggest a significant coupling between the
electronic and lattice degrees of freedom in Te. A long-lived shift of the
absorption edge suggests a metastable excited state of Te in a new equilibrium
potential energy surface that lives on the order of the carrier recombination
timescale. The observed phonon-induced oscillations of the hot carriers are
supportive of a semiconductor-to-metal light-induced phase transition, whereby
Te becomes more metallic with increasing phonon-induced displacement.
Additionally, near the Fermi level we observe an energy-dependent phase of the
displacive excitation of the A$_{rm{1g}}$ phonon mode. The discovery of
coherent coupling between the lattice and hot carriers in Te provides the basis
to investigate coherent interactions between spin and orbital degrees of
freedom. The results spectrally and temporally resolve the correlation between
photo-excited hot carriers and coherent lattice excitations, providing insight
on the optical manipulation of the tellurium electronic structure at high
carrier densities exceeding $10^{21},mathrm{cm}^{-3}$.
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