Ultrafast photoinduced band splitting and carrier dynamics in chiral tellurium nanosheets

Abstract

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 H 4 and H 5 and the degenerate H 6 valence bands (VB) and the lowest degenerate H 6 conduction band (CB) as well as a higher energy transition at the Lpoint. Surprisingly, the degeneracy of the H 6 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 the 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.

Mid- and Far-Infrared Supercontinuum Generation in Bulk Tellurium Spanning from 5.3 $μ$m to 32 $μ$m

“…3. The anisotropy of the Raman response in Te has recently been reported in [27]. For E c, the response is weaker compared to E⊥c but this alone cannot explain the stark contrast we see in experiment.…”

Study of the Growth Mechanism of Solution‐Synthesized Symmetric Tellurium Nanoflakes at Atomic Resolution

“…Recently, as a new member of 2D materials, 2D Te has drawn much attention from researchers. Theoretical calculations and experiments reveal its promising physical and chemical properties, [ 17–24 ] such as high carrier mobilities, [ 17–19 ] tunable bandgap (which is inversely proportional to the number of layers), [ 18,20 ] and good air‐stability at room temperature, [ 18,20,21 ] which make it a potential candidate for applications in electronics and optoelectronic devices. Nanodevices based on 2D Te have been reported to achieve outstanding performance.…”

Ultrafast Thermalization Pathways of Excited Bulk and Surface States in the Ferroelectric Rashba Semiconductor GeTe

“…Finally, in order to identify which individual scattering channels are predominantly responsible for the contrasting temperature dependence of the thermalization pathways within the electronic subsystem and between the electronic subsystem and the lattice, we performed theoretical calculations within the Boltzmann approach including all types of elementary scatterings. [66][67][68] Among several existing stateof-the-art theoretical methods that have proven successful for describing nonequilibrium dynamics of excited states, such as real-time time-dependent density-functional theory (RTTD-DFT) [69] and other types of nonequilibrium DFT calculations, [70] the Boltzmann approach is a relatively inexpensive and very powerful method to identify in detail which individual scattering channels drive the different thermalization pathways. [66][67][68] To this end, we computed the temperature dependence of the scattering rates for all electron-electron and electron-phonon scatterings that can be obtained from the Boltzmann scattering equation when combining the bulk (BS) and surface (SS1, SS2) transient Rashba bands with a single effective phonon band.…”