S. S. Tsirkin

Band structure engineering in topological insulator based heterostructures.

The ability to engineer an electronic band structure of topological insulators would allow the production of topological materials with tailor-made properties. Using ab initio calculations, we show a promising way to control the conducting surface state in topological insulator based heterostructures representing an insulator ultrathin films on the topological insulator substrates. Because of a specific relation between work functions and band gaps of the topological insulator substrate and the insulator ultrathin film overlayer, a sizable shift of the Dirac point occurs resulting in a significant increase in the number of the topological surface state charge carriers as compared to that of the substrate itself. Such an effect can also be realized by applying the external electric field that allows a gradual tuning of the topological surface state. A simultaneous use of both approaches makes it possible to obtain a topological insulator based heterostructure with a highly tunable topological surface state.

Dependence of the Intrinsic Line Width of Surface States on the Wave Vector: The Cu(111) and Ag(111) Surfaces

The dependence of the intrinsic line width Γ of electron and hole states due to inelastic scattering on the wave vector k∥ in the occupied surface state and the first image potential state on the Cu(111) and Ag(111) surfaces has been calculated using the GW approximation, which simulates the self-energy of the quasiparticles by the product of the Greens’s function and the dynamically screened Coulomb potential. Different contributions to the relaxation of electron and hole excitations have been analyzed. It has been demonstrated that, for both surfaces, the main channel of relaxation of holes in the occupied surface states is intraband scattering and that, for electrons in the image potential states, the interband transitions play a decisive role. A sharp decrease in the intrinsic line width of the hole state with an increase in k∥ is caused by a decrease in the number of final states, whereas an increase in Γ of the image potential state is predominantly determined by an increase of its overlap with bulk states.

Inelastic decay of electrons in Shockley-type metal-organic interface states

We present a theoretical study of lifetimes of interface states (IS) on metal-organic interfaces PTCDA/Ag(111), NTCDA/Ag(111), PFP/Ag(111), and PTCDA/Ag(100), describing and explaining the recent experimental data. By means of unfolding the band structure of one of the interfaces under study onto the Ag(111) Brillouin zone we demonstrate, that the Brillouin zone folding upon organic monolayer deposition plays a minor role in the phase space for electron decay, and hence weakly affects the resulting lifetimes. The presence of the unoccupied molecular states below the IS gives a small contribution to the IS decay rate mostly determined by the change of the phase space of bulk states upon the energy shift of the IS. The calculated lifetimes follow the experimentally observed trends. In particular, we explain the trend of the unusual increase of the IS lifetimes with rising temperature.

Model pseudopotential for the Cu(110) surface

A method has been proposed for constructing the two-dimensional pseudopotential describing the electronic structure of the Cu(110) surface. This method can also be applied to construct the corresponding pseudopotentials for the (110) surface of a number of other face-centered cubic metals, such as Ag, Au, Al, Pd, and Pt. The electronic structure obtained can be used for fast calculations of single-particle and collective electron excitations both on the pure Cu(110) surface and on the surface covered with adatoms or ultrathin films of other metals.

On different mechanisms of electron-phonon scattering of electron and hole excitations on an Ag(110) surface

AbstractWe present the results of a detailed theoretical study of the electron-phonon scattering of electron and hole excitations in the unoccupied and occupied surface states on an Ag(110) surface. We show that the electron-phonon coupling parameter λ in the unoccupied surface state is approximately three times smaller than that in the occupied one, because the scattering of these states is determined by different phonon modes. The difference in the phonon-induced decay mechanisms of electron and hole excitations is determined by different spatial localizations of the unoccupied and occupied surface states at the

Contribution of phonons to the line width of surface electronic states on Pd(111)

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Visualizing spin-dependent bulk scattering and breakdown of the linear dispersion relation in Bi2Te3

point of the two-dimensional Brillouin zone.

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

The contribution of inelastic electron-electron scattering to the decay rate of excitations in the surface states and first two image potential states at the Ȳ point on the surface is calculated in the GW approximation, and the quasi-momentum dependence of the corresponding contribution for the surface states is analyzed. The mechanisms of electron scattering in these states are studied, and the temperature dependence of the excitation lifetime is analyzed with allowance for the contribution of the electron-phonon interaction calculated earlier.