Variation of the character of spin-orbit interaction by Pt intercalation underneath graphene on Ir(111)

The modification of the graphene spin structure is of interest for novel possibilities of application of graphene in spintronics. The most exciting of them demand not only high value of spin-orbit splitting of the graphene states, but non-Rashba behavior of the splitting and spatial modulation of the spin-orbit interaction. In this work we study the spin and electronic structure of graphene on Ir(111) with intercalated Pt monolayer. Pt interlayer does not change the 9.3×9.3 superlattice of graphene, while the spin structure of the Dirac cone becomes modified. It is shown that the Rashba splitting of the π state is reduced, while hybridization of the graphene and substrate states leads to a spin-dependent avoided-crossing effect near the Fermi level. Such a variation of spin-orbit interaction combined with the superlattice effects can induce a topological phase in graphene

Specific features of the electronic, spin, and atomic structures of a topological insulator Bi2Te2.4Se0.6

The specific features of the electronic and spin structures of a triple topological insulator Bi2Te2.4Se0.6, which is characterized by high-efficiency thermoelectric properties, have been studied with the use of angular- and spin-resolved photoelectron spectroscopy and compared with theoretical calculations in the framework of the density functional theory. It has been shown that the Fermi level for Bi2Te2.4Se0.6 falls outside the band gap and traverses the topological surface state (the Dirac cone). Theoretical calculations of the electronic structure of the surface have demonstrated that the character of distribution of Se atoms on the Te–Se sublattice practically does not influence the dispersion of the surface topological electronic state. The spin structure of this state is characterized by helical spin polarization. Analysis of the Bi2Te2.4Se0.6 surface by scanning tunnel microscopy has revealed atomic smoothness of the surface of a sample cleaved in an ultrahigh vacuum, with a lattice constant of ~4.23 Å. Stability of the Dirac cone of the Bi2Te2.4Se0.6 compound to deposition of a Pt monolayer on the surface is shown.This study was supported by the Ministry of Education and Science of the Russian Federation, the St. Petersburg State University (project nos. 11.38.271.2014 and 15.61.202.2015), and the Russian Foundation for Basic Research (project nos. 12-02-00226, 13-02-91327, 14-08-31110, and 13-02-12110). The research was also performed at the Resource Center “Physical Methods of Surface Investigation” at St. Petersburg State University. We are also grateful to collaborators of the Helmholtz-Zentrum (Berlin) for financial and technical support.Peer reviewe

Nontrivial spin structure of graphene on Pt(111) at the Fermi level due to spin-dependent hybridization

The electronic and spin structure of a graphene monolayer synthesized on Pt(111) has been investigated experimentally by angle- and spin-resolved photoemission with different polarizations of incident synchrotron radiation and using density functional theory calculations. It is shown that despite the observed total quasifreestanding character of the dispersion of the graphene π state remarkable local distortions and breaks in the dispersions take place due to hybridization between the graphene π and Pt d states. Corresponding spin-dependent avoided-crossing effects lead to significant modification of the spin structure and cause an enhanced induced spin-orbit splitting of the graphene π states near the Fermi level in the region of the K¯ point of the graphene Brillouin zone (BZ) with a magnitude of 80-200 meV depending on the direction in the BZ. Using p, s, and elliptical polarizations of the synchrotron radiation, the contributions of the graphene π and Pt d states were separated and their intersection at the Fermi level, which is important for effective spin injection between these states, was shown. Moreover, analysis of the data allows us to conclude that in the region of the Dirac point the spin structure of the system cannot be described by a Rashba splitting, and even a spin-orbit gap between lower and upper Dirac cones is observed.The work was partially supported by a grant of Saint Petersburg State University for scientific investigations (Grant No. 11.38.271.2014) and Russian Foundation for Basic Research (RFBR) projects (Project No. 13-02-91327) and performed within the framework of collaboration between the Deutsche Forschungsgemeinschaft and Russian Foundation for Basic Research (Grant No. RA 1041/3-1). We acknowledge the financial support of the University of Basque Country UPV/EHU (Grant No. GIC07-IT-756-13), the Departamento de Educacion del Gobierno Vasco and the Spanish Ministerio de Ciencia e Innovacion (Grant No. FIS2010-19609-C02-01), Project FIS2013-48286-C2-1-P of the Spanish Ministry of Economy and Competitiveness MINECO, and the Tomsk State University Competitiveness Improvement Program.Peer Reviewe

Influence of the surface reorganization on the spin electronic structure of the Dirac cone of topological insulators

Resumen del trabajo presentado al New Trends in Topological Insulators (NTTI), celebrado en Donostia-San Sebastián (España) del 6 al10 de julio de 2015.Peer reviewe

Modification of atomic, electronic and spin structure of Pb-based quaternary topological insulator with various stoichiometry

Resumen del trabajo presentado al New Trends in Topological Insulators (NTTI), celebrado en Donostia-San Sebastián (España) del 6 al10 de julio de 2015.Peer reviewe

Variation of the character of spin-orbit interaction by Pt intercalation underneath graphene on Ir(111)

The modification of the graphene spin structure is of interest for novel possibilities of application of graphene in spintronics. The most exciting of them demand not only high value of spin-orbit splitting of the graphene states, but non-Rashba behavior of the splitting and spatial modulation of the spin-orbit interaction. In this work we study the spin and electronic structure of graphene on Ir(111) with intercalated Pt monolayer. Pt interlayer does not change the 9.3×9.3 superlattice of graphene, while the spin structure of the Dirac cone becomes modified. It is shown that the Rashba splitting of the π state is reduced, while hybridization of the graphene and substrate states leads to a spin-dependent avoided-crossing effect near the Fermi level. Such a variation of spin-orbit interaction combined with the superlattice effects can induce a topological phase in graphene

Spin and electronic structure of the topological insulator Bi1.5Sb0.5Te1.8Se1.2

Electronic and spin structure of the Dirac-cone-like topological surface and valence band states were studied experimentally and theoretically for topological insulator with fractional stoichiometry Bi1.5Sb0.5Te1.8Se1.2 which is considered as one of the best candidates for efficient spin-polarized current generation. By means of spin- and angle-resolved photoelectron spectroscopy we demonstrate the separation of the Dirac point from the bulk states and the helical spin structure of the Dirac cone. For the freshly cleaved surface the Fermi level is located in the bulk band gap and an exposure in residual gases shifts the Fermi level towards the bulk conduction band. Results of the theoretical calculations are in a good agreement with the experimental data. Surface morphology study shows a well-structured atomically sharp surface after cleavage. The transport measurements confirm that this topological insulator has relatively high resistance with semiconductor-like temperature dependence at low temperatures. The studied Bi1.5Sb0.5Te1.8Se1.2 crystals demonstrated a quite large Seebeck coefficient values reaching −400 μV/K at room temperature

Magneto-spin−orbit graphene: Interplay between exchange and spin−orbit couplings

A rich class of spintronics-relevant phenomena require implementation of robust magnetism and/or strong spin-orbit coupling (SOC) to graphene, but both properties are completely alien to it. Here, we for the first time experimentally demonstrate that a quasi-freestanding character, strong exchange splitting and giant SOC are perfectly achievable in graphene at once. Using angle- and spin-resolved photoemission spectroscopy, we show that the Dirac state in the Au-intercalated graphene on Co(0001) experiences giant splitting (up to 0.2 eV) while being by no means distorted due to interaction with the substrate. Our calculations, based on the density functional theory, reveal the splitting to stem from the combined action of the Co thin film in-plane exchange field and Au-induced Rashba SOC. Scanning tunneling microscopy data suggest that the peculiar reconstruction of the Au/Co(0001) interface is responsible for the exchange field transfer to graphene. The realization of this "magneto-spin-orbit" version of graphene opens new frontiers for both applied and fundamental studies using its unusual electronic bandstructure.The authors acknowledge support by the Saint Petersburg State University (Grant 15.61.202.2015), German-Russian Interdisciplinary Science Center (G-RISC) funded by the German Federal Foreign Office via the German Academic Exchange Service (DAAD) and Russian-German laboratory at BESSY II (Helmholtz-Zentrum Berlin). The funding by the University of the Basque Country (Grants GIC07IT36607 and IT-756-13), the Spanish Ministry of Science and Innovation (Grants FIS2013-48286-C02-02-P, FIS2013-48286-C02-01-P, and FIS2016-75862-P) and Tomsk State University competitiveness improvement programme (Project No. 8.1.01.2017) is also gratefully acknowledged. I.P.R. acknowledges support by the Ministry of Education and Science of the Russian Federation within the framework of the governmental program “Megagrants” (state task no. 3.8895.2017/P220).Peer reviewe