are protected by time-reversal symmetry (TRS) and characterized by a nonzero Z 2 invariant. [1] The spin and momentum of topological edge states (2D TIs) or surface states (3D TIs) are orthogonally locked and robust against nonmagnetic backscattering. [2] Beyond the Z 2 -order protected band topology, the crystalline symmetry preserves the band topology in cases such as discrete rotation and mirror symmetry which defines the topological crystalline insulators (TCIs). [3] A combination of these two topological properties in one material, i.e., dual topology, defines a dual TI and offers fertile possibilities of gapping one topological surface state via breaking the respective symmetry while preserving another. [4] Therefore, the exploration of dual TIs can elucidate more degrees of freedom to manipulate the band structure and electric transport properties for designing novel topological electronic, spintronic, thermoelectric, and optical devices. [5] Dual TIs can exist in different topological forms. [6] One form refers to dual protection of surface states by multiple bulk symmetries, such as Bi 2 Te 3 [6b] predicted to be both a TI and a TCI whose topological surface state is protected by TRS and crystal symmetry simultaneously. Another interesting form is that the dual TIs can Dual topological insulators, simultaneously protected by time-reversal symmetry and crystalline symmetry, open great opportunities to explore different symmetry-protected metallic surface states. However, the conventional dual topological states located on different facets hinder integration into planar opto-electronic/spintronic devices. Here, dual topological superlattices (TSLs) Bi 2 Se 3 -(Bi 2 /Bi 2 Se 3 ) N with limited stacking layer number N are constructed. Angle-resolved photoelectron emission spectra of the TSLs identify the co existence and adjustment of dual topological surface states on Bi 2 Se 3 facet. The existence and tunability of spin-polarized dual-topological bands with N on Bi 2 Se 3 facet result in an unconventionally weak antilocalization effect (WAL) with variable WAL coefficient α (maximum close to 3/2) from quantum transport experiments. Most importantly, it is identified that the spin-polarized surface electrons from dual topological bands exhibit circularly and linearly polarized photogalvanic effect (CPGE and LPGE). It is anticipated that the stacked dual-topology and stacking layer number controlled bands evolution provide a platform for realizing intrinsic CPGE and LPGE. The results show that the surface electronic structure of the dual TSLs is highly tunable and well-regulated for quantum transport and photoexcitation, which shed light on engineering for opto-electronic/spintronic applications.
Single-particle band theory has been very successful in describing the band structure of topological insulators. However, with decreasing thickness of topological insulator thin films, single-particle band theory is insufficient to explain their band structures and transport properties due to the existence of top and bottom surface-state coupling. Here, we reconstruct this coupling with an equivalently screened Coulomb interaction in Bi2Se3 ultrathin films. The thickness-dependent position of the Dirac point and the magnitude of the mass gap are discussed in terms of the Hartree approximation and the self-consistent gap equation. We find that for thicknesses below 6 quintuple layers, the magnitude of the mass gap is in good agreement with the experimental results. Our work provides a more accurate means of describing and predicting the behaviour of quasi-particles in ultrathin topological insulator films and stacked topological systems.
Ferroelectric Rashba semiconductor α-GeTe provides a promising arena in spintronics due to its large bulk and surface Rashba. Since most surface Rashba bands are located above Fermi level, the spin dynamics are mainly dominated by bulk states. Whether the surface states of α-GeTe can modulate the spin dynamics or not is an open question. Here, we report the manipulation of magnetic damping by the surface states of α-GeTe via ferromagnetic resonance (FMR) and theory calculation. The surface states located near the Fermi level of α-GeTe is realized by doping Bi atoms and revealed by angle-resolved photoemission spectroscopy (ARPES). Moreover, the magnitude of magnetic damping is related to the density of states near Fermi surfaces of Ge1 − xBixTe. Our work improves the understanding of the magnetic damping influenced by different part of Rashba bands and gives a platform for the research of α-GeTe in Rashba effect and the spintronics.
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