Kavli Affiliate: Peidong Yang
| First 5 Authors: Jonah R. Adelman, Hugo Laurell, Lauren B. 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 it’s 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$_{rm{1}}$ 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 an 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 change in the metallicity, 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$_{rm{1}}$ 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 Te electronic
structure at high carrier densities exceeding $10^{21},mathrm{cm}^{-3}$.
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