  Trigonal tellurium (Te) is a chiral semiconductor that lacks both mirror and
inversion symmetries, resulting in complex band structures with Weyl crossings
and unique spin textures. Detailed time-resolved polarized reflectance
spectroscopy is used to investigate its band structure and carrier dynamics.
The polarized transient spectra reveal optical transitions between the
uppermost spin-split H4 and H5 and the degenerate H6 valence bands (VB) and the
lowest degenerate H6 conduction band (CB) as well as a higher energy transition
at the L-point. Surprisingly, the degeneracy of the H6 CB (a proposed Weyl
node) is lifted and the spin-split VB gap is reduced upon photoexcitation
before relaxing to equilibrium as the carriers decay. Using ab initio density
functional theory (DFT) calculations we conclude that the dynamic band
structure is caused by a photoinduced shear strain in the Te film that breaks
the screw symmetry of the crystal. The band-edge anisotropy is also reflected
in the hot carrier decay rate, which is a factor of two slower along c-axis
than perpendicular to it. The majority of photoexcited carriers near the
band-edge are seen to recombine within 30 ps while higher lying transitions
observed near 1.2 eV appear to have substantially longer lifetimes, potentially
due to contributions of intervalley processes in the recombination rate. These
new findings shed light on the strong correlation between photoinduced carriers
and electronic structure in anisotropic crystals, which opens a potential
pathway for designing novel Te-based devices that take advantage of the
topological structures as well as strong spin-related properties.
