The peculiarities of halogens adsorption on A3B5(001) surface

Theoretical study of the F, Cl, Br, I adsorption on GaAs(001) surface is presented. The most stable configurations of halogens on Ga-rich ζ-(4×2) reconstruction are determined with increasing of adatoms concentration. The bonds weakening is found more significant for the F and Cl atoms which can induce stationary etching whereas I-induced changes in Ga-As binding energy is not sizable and its adsorption lead to the surface passivation

Circular dichroism and superdiffusive transport at the surface of BiTeI

et al.We investigate the electronic states of BiTeI after the optical pumping with circularly polarized photons. Our data show that photoexcited electrons reach an internal thermalization within 300 fs of the arrival of the pump pulse. Instead, the dichroic contrast generated by the circularly polarized light relaxes on a time scale shorter than 80 fs. This result implies that orbital and spin polarization created by the circular pump pulse rapidly decays via manybody interaction. The persistent dichroism at longer delay times is due to the helicity dependence of superdiffussive transport. We ascribe it to the lack of inversion symmetry in an electronic system far from equilibrium conditions.We acknowledge that the FemtoARPES project was financially supported by the RTRA Triangle de la Physique, and the ANR program Chaires d’Excellence (Nr. ANR-08-CEXCEC8-011-01).Peer Reviewe

Unoccupied Topological States on Bismuth Chalcogenides

The unoccupied part of the band structure of topological insulators Bi$_2$Te$_{x}$Se$_{3-x}$ ($x=0,2,3$) is studied by angle-resolved two-photon photoemission and density functional theory. For all surfaces linearly-dispersing surface states are found at the center of the surface Brillouin zone at energies around 1.3 eV above the Fermi level. Theoretical analysis shows that this feature appears in a spin-orbit-interaction induced and inverted local energy gap. This inversion is insensitive to variation of electronic and structural parameters in Bi$_2$Se$_3$ and Bi$_2$Te$_2$Se. In Bi$_2$Te$_3$ small structural variations can change the character of the local energy gap depending on which an unoccupied Dirac state does or does not exist. Circular dichroism measurements confirm the expected spin texture. From these findings we assign the observed state to an unoccupied topological surface state

Termination-dependent surface properties in the giant-Rashba semiconductors BiTeX (X=Cl, Br, I)

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).The noncentrosymmetric semiconductors BiTeX(X=Cl,Br,I) show large Rashba-type spin-orbit splittings in their electronic structure making them candidate materials for spin-based electronics. However, BiTeI(0001) single-crystal surfaces usually consist of stacking-fault-induced domains of Te and I terminations implying a spatially inhomogeneous electronic structure. Here we combine scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), and density functional theory calculations to systematically investigate the structural and electronic properties of BiTeX(0001) surfaces. For X=Cl, Br we observe macroscopic single-terminated surfaces. We discuss chemical characteristics among the three materials in terms of bonding character, surface electronic structure, and surface morphology.This work was financially supported by the Deutsche Forschungsgemeinschaft through FOR1162 and partly by the Ministry of Education and Science of Russian Federation (Grant No. 2.8575.2013), the Russian Foundation for Basic Research (Grants No. 15-02-01797 and No. 15-02-02717), and Saint Petersburg State University (Project No. 11.50.202.2015).Peer Reviewe

Defect and structural imperfection effects on the electronic properties of BiTeI surfaces

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.-- et al.The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ∼100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability.This work was financially supported by the Deutsche Forschungsgemeinschaft through FOR1162 and the Bundesministerium für Bildung und Forschung (grant numbers 05K10WW1/2 and 05KS1WMB/1). TVK and VIG acknowledge partial support from the Government of Sverdlovsk Region and Russian Foundation for Basic Research (grant no. 13-02-96046_Ural) and the Ural Branch of the Russian Academy of Sciences (grant no. 12-U-2-1002). This publication was funded by the Deutsche Forschungsgemeinschaft and the University of Würzburg in the funding programme Open Access Publishing.Peer Reviewe