S. V. Eremeev

Ideal Two-Dimensional Electron Systems with a Giant Rashba-Type Spin Splitting in Real Materials: Surfaces of Bismuth Tellurohalides

Spintronics is aimed at actively controlling and manipulating the spin degrees of freedom in semiconductor devices. A promising way to achieve this goal is to make use of the tunable Rashba effect that relies on the spin-orbit interaction in a two-dimensional electron system immersed in an inversion-asymmetric environment. The spin-orbit-induced spin splitting of the two-dimensional electron state provides a basis for many theoretically proposed spintronic devices. However, the lack of semiconductors with large Rashba effect hinders realization of these devices in actual practice. Here we report on a giant Rashba-type spin splitting in two-dimensional electron systems that reside at tellurium-terminated surfaces of bismuth tellurohalides. Among these semiconductors, BiTeCl stands out for its isotropic metallic surface-state band with the Γ-point energy lying deep inside the bulk band gap. The giant spin splitting of this band ensures a substantial spin asymmetry of the inelastic mean free path of quasiparticles with different spin orientations.

Disentanglement of Surface and Bulk Rashba Spin Splittings in Noncentrosymmetric BiTeI

BiTeI has a layered and non-centrosymmetric structure where strong spin-orbit interaction leads to a giant spin splitting in the bulk bands. Here we present high-resolution angle-resolved photoemission (ARPES) data in the UV and soft x-ray regime that clearly disentangle the surface from the bulk electronic structure. Spin-resolved UV-ARPES measurements on opposite, nonequivalent surfaces show identical spin structures, thus clarifying the surface state character. Soft x-ray ARPES data clearly reveal the spindle-torus shape of the bulk Fermi surface, induced by the spin-orbit interaction. PACS numbers: 71.20.Nr, 71.70.Ej, 79.60.Bm 1 ar X iv :1 20 4. 21 96 v1 [ co nd -m at .m tr lsc i] 1 0 A pr 2 01 2 The breaking of inversion symmetry and its influence on the spin structure of surface states under action of spin–orbit interaction (SOI) has been extensively studied in recent years [1, 2]. The main finding is that the surface states become spin-split according to the Rashba model [3] resulting in two spin-polarized concentric Fermi contours. The lack of inversion symmetry in the bulk crystal structure is expected to induce a spin splitting with a more complex bandand spin-structure. Combined with strong SOI the Fermi surface can take the shape of a torus [4]. For non-centrosymmetric superconductors such as for example CePt3Si [5] this peculiar band structure is expected to result in topologically protected spin polarized edge states reminiscent of Majorana modes [6]. Recently, an ARPES and spin-resolved ARPES study by Ishizaka et al. [7] proposed that the semiconductor BiTeI features a very large spin-splitting, arising from the broken inversion symmetry in the crystal bulk and a strong SOI. Theoretical work based on the perturbative k ·p formalism linked the unusually large spin splitting in BiTeI to the negative crystal field splitting of the top valence bands [8]. Optical transition measurements [9] are in accordance with the giant bulk spin-splitting of the gap defining valence and conduction bands predicted by first principle calculations [7, 8]. In addition it was shown in recent theoretical work that BiTeI can become a topological insulator under action of hydrostatic pressure [10], and thus is closely related to non-centrosymmetric topological superconductors. The present study provides first band mapping of a system without bulk inversion symmetry and giant SOI by the example of BiTeI, featuring a three-dimensional Rashba splitting of the bulk bands. Further it is shown that the Rashba-split state observed for this material in the UV photon energy regime is not a quantum well state [7] but rather a surface state, using a simple symmetry argument based on spin-resolved ARPES (SARPES) measurements, which is confirmed by first principle calculations. All measurements were performed at the Swiss Light Source of the Paul-Scherrer-Institut. The SARPES data was measured with the Mott polarimeter at the COPHEE endstation [11] of the Surface and Interface Spectroscopy beamline at a photon energy of 24 eV. The spin-integrated data at photon energies 20-63 eV were taken at the high-resolution ARPES endstation at the same beamline. The soft x-ray ARPES data were taken at the SX-ARPES endstation of the ADRESS beamline at photon energies of 310-850 eV. All spin-integrated measurements were performed at a sample temperature of 11 K and a base pressure lower than 10−10 mbar, the SARPES data was taken at 20 K.

Effect of the atomic composition of the surface on the electron surface states in topological insulators A2VB3VI

The results of the theoretical investigation of the surface electronic structure of A2VB3VI compounds containing topologically protected surface states are reported. The ideal Bi2Te3, Bi2Se3, and Sb2Te3 surfaces and surfaces with an absent external layer of chalcogen atoms, which were observed experimentally as monolayer terraces, have been considered. It has been shown that the discrepancy between the calculated Fermi level and the value measured in the photoemission experiments can be attributed to the presence of the “dangling bond” states on the surface of the terraces formed by semimetal atoms. The fraction of such terraces on the surface has been estimated.

Ternary Compounds Based on Binary Topological Insulators As an Efficient Way for Modifying the Dirac Cone

The electronic structure of AIVBVI · A2VB3VI ternary compounds consisting of seven-layer atomic blocks separated by van der Waals gaps has been theoretically investigated. The YbBi(Sb)2Te4 compounds have been considered, for which a similar atomic structure has been predicted. It has been shown that most compounds based on Group IV elements, as well as YbBi2Te4, are three-dimensional topological insulators. Calculations of the surface electronic structure of MBi2Te4, where M is a Group IV element or Yb, demonstrate the possibility of tuning the Dirac surface conduction state owing to the first element.

Ternary thallium-based semimetal chalcogenides Tl-V-VI2 as a new class of three-dimensional topological insulators

AbstractThe results of the theoretical investigation of the bulk and surface electronic structures of Tl-V-VI2 compounds, where V is the Bi or Sb semimetal and VI is the Se or Te chalcogen, are reported. It has been shown that these compounds are three-dimensional topological insulators. Both a topologically protected surface state, which forms a Dirac cone at the

Giant Rashba-type spin splitting at polar surfaces of BiTeI

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Electron–phonon contribution to the phonon and excited electron (hole) linewidths in bulk Pd

point, and occupied surface states, which are localized in the band gap, are present on the surface of these compounds.

Hydrogen adsorption on Pd/TiFe (110) surface

The ab initio calculations of the electronic structure in the bulk and at the (0001) surface of narrow-band Bi2Se3, Sb2Te3, Sb2STe3, and Sb2SeTe2 semiconductors have been performed. It has been shown that ternary compounds Sb2STe2 and Sb2SeTe2, as well as the previously known compounds Bi2Se3 and Sb2Te3, are three-dimensional topological insulators. The influence of the subsurface van der Waals gap expansion on the surface electronic structure of these compounds has been analyzed. It has been shown that this expansion leads to the formation of new (trivial) surface states, namely a parabolic state in the conduction band and an M-shaped state in the valence band. These results explain the phenomena discovered recently in photoemission experiments and reveal the nature of new states that are caused by the adsorption of atoms on the surfaces of the layered topological insulators.