Topological surface states in epitaxial (SnBi2Te4)n(Bi2Te3

Ultrafast Spin‐Charge Conversion at SnBi2Te4/Co Topological Insulator Interfaces Probed by Terahertz Emission Spectroscopy

“…Details of the epitaxial growth and material characterization may be found in Section S1, Supporting Information and ref. [14].…”

“…However, for SnBi 2 Te 4 thickness larger than 5 SL, the gap closes due to an overlap between conduction and the valence band. [14] Specially prepared sample 5 SL SnBi 2 Te 4 with a 20 nm thick Te capping was measured at the "CASSIOPEE" beamline of SOLEIL synchrotron facility after capping removal, with horizontally polarized light and a photon energy of 27 eV in order to visualize the band structure and the Fermi surface of SnBi 2 Te 4 . The measurements were carried out at the temperature of 15 K and an energy resolution of 15 meV with a polar angle step of 0.2°.…”

“…For this goal, we have estimated the bulk conductivity of SnBi 2 Te 4 in the vicinity of 2.35 × 10 5 Ω −1 . m −1 via Hall effect measurements [14] (more details on the procedure www.advopticalmat.de are available in Section S4, Supporting Information). E THz are about equal in peak-to-peak amplitude revealing two specific features compared to SnBi 2 Te 4 (5SL)/Co(4)/AlO x (3): i) the THz polarization is reversed, showing now a predominant signal from ISHE of Pt (dual SCC occurs here with both ISHE in Pt and expected interfacial SCC for SnBi 2 Te 4 /Co) and ii) renormalized E THz emission of SnBi 2 Te 4 (5SL)/Co(2) is estimated around 20% of the one of Co/Pt.…”

“…The microstructure of SnBi 2 Te 4 septuple layers (SL) was investigated by cross‐sectional high‐resolution scanning transmission electron spectroscopy (HR‐STEM ‐not shown‐). [ 14 ] In contrast to Bi 2 Te 3 quintuple layer (QL) structures, SnBi 2 Te 4 data show a layered structure consisting of seven atom rows, four occupied by Te atoms and the rest by the metal atoms Bi and Sn as illustrated in Figure . The septuple layer structure of SnBi 2 Te 4 was also confirmed by X‐ray diffraction (XRD) where a pure phase of seven‐layers stacking is confirmed over the entire film, indicating a tendency to form an ordered alloy where Sn ideally occupies the middle row.…”

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technological interests lie in spin-orbit torque (SOT) phenomena for magnetic commutation [5][6][7] or ultrafast terahertz (THz) wave emission. [8] In this prospect, topological insulators [4,9] (TIs) and their topological surface states (TSS), in particular those based on Bi compounds such as Bi 2 Se 3 , [10] Bi 2 Te 3 , [11,12] SnBi 2 Te 4 , [13,14] Bi 1−x Sb x , [15][16][17] or α-Sn, [18,19] currently represent strong potential candidates to fulfill these applications. Indeed, such TIs or Dirac materials are known to provide very efficient SCC owing to the presence of topologically-protected surface states and spin momentum locking (SML) at their surfaces.

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