Abstract
Topological phases of matter offer exciting possibilities to realize lossless charge and spin information transport on ultrafast time scales. However, this requires detailed knowledge of their nonequilibrium properties. Here, we employ time-, spin- and angle-resolved photoemission to investigate the ultrafast response of the Sb(111) spin-polarized surface state to femtosecond-laser excitation. The surface state exhibits a giant mass enhancement which is observed as a kink structure in its energy-momentum dispersion above the Fermi level. The kink structure, originating from the direct coupling of the surface state to the bulk continuum, is characterized by an abrupt change in the group velocity by ~70%, in agreement with our GW-based band structure calculations. Our observation of this connectivity in the transiently occupied band structure enables the unambiguous experimental verification of the topological nature of the surface state. The influence of bulk-surface coupling is further confirmed by our measurements of the electron dynamics, which show that bulk and surface states behave as a single thermalizing electronic population with distinct contributions from low-k electron-electron and high-k electron-phonon scatterings. These findings are important for future applications of topological semimetals and their excitations in ultrafast spintronics.
Highlights
Topological phases of matter offer exciting possibilities to realize lossless charge and spin information transport on ultrafast time scales
Understanding the elementary scattering processes which govern the ultrafast response of topological states of matter to femtosecond-laser excitation is crucial for applications in ultrafast spintronics and opto-spintronics[1,2,3,4]
We performed tr-angleresolved photoemission (ARPES) experiments on Sb(111) single crystals using pump and probe femtosecond laser pulses of 1.5 and 6 eV photon energy under the experimental geometry shown in Fig. 1a
Summary
Topological phases of matter offer exciting possibilities to realize lossless charge and spin information transport on ultrafast time scales. For Sb2Te3, it was shown how it leads to relatively small changes in the linear band dispersion of the surface state near its connectivity points with the bulk valence bands below EF27 Such an unexpectedly weak bulk-surface coupling was confirmed in magnetotransport experiments[33], and by the observation that the connectivity between bulk and surface bands is mediated by bulk-derived surface resonances exhibiting a reversed spin texture with respect to that of the topological surface state in Bi2Te334 and Bi2Se335. This scenario was further confirmed by measurements of the electron dynamics, which revealed a highly decoupled surface and bulk state dynamics following ultrafast optical excitation[35]
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