Quasiparticle interference patterns measured by scanning tunneling microscopy can be used to study the local electronic structure of metal surfaces and high-temperature superconductors. Here, we show that even in nonmagnetic systems the spin of the quasiparticles can have a profound effect on the interference patterns. On Bi(110), where the surface state bands are not spin degenerate, the patterns are not related to the dispersion of the electronic states in a simple way. In fact, the features which are expected for the spin-independent situation are absent and the observed interference patterns can be interpreted only by taking spin-conserving scattering events into account.
The electronic and structural properties of thin epitaxial Mn films on Si(111)-(7 × 7) and their silicide reaction are studied by means of low-energy electron diffraction, scanning tunnelling microscopy (STM) and photoemission spectroscopy (PES). The deposition of Mn at room temperature initially results in the growth of islands. The metal–silicon reaction already occurs at this temperature, which is further enhanced by annealing up to 400°C, leading to the formation of manganese silicide and turning islands into nearly closed films at higher coverage. A pseudo-(1 × 1) phase develops for Mn films of up to 1 monolayer (ML) thickness. For films of higher thicknesses of up to 5 ML, a ( )R30° phase is observed. STM images show that then the silicide film is almost closed and exhibits a strain relief network reflecting an incommensurate interface structure. PES reveals that the (1 × 1) phase is semiconducting while the ( )R30° phase is metallic. For both phases, Si 2p core level photoemission data indicate that the surface is probably terminated by Si atoms.
Electronic structure investigations of Cu͑554͒ using low-temperature scanning tunneling microscopy/ spectroscopy indicate that the dimensionality of the ͑111͒-derived surface state changes from two dimensions to one dimension when the electron energy and wave vector comply with the lateral confinement conditions of the individual terrace. Moreover, an alternative explanation can be given for the gradual changeover from terrace to step modulation with an increasing miscut angle reported in earlier photoemission experiments.
The apparent contradiction of one-dimensional adsorbate chains on Si͑111͒ having a 3ϫ2 unit cell and yet a 3ϫ1 diffraction pattern is resolved for the example of Ba/Si(111)-(3ϫ2). Random registry shifts between adsorbate chains are observed in tunneling microscopy, with very short interchain correlation lengths. Fourier analysis provides a natural explanation for a pseudo-(3ϫ1) diffraction pattern. Within density-functional theory such registry shifts can occur with essentially negligible energy cost, leading to entropy-driven, virtually perfect disorder. Substrate states of high symmetry and one-dimensional character are inferred to promote this phenomenon.
We demonstrate that bulk band structure can have a strong influence in scanning tunneling microscopy measurements by resolving electronic interference patterns associated with scattering phenomena of bulk states at a metal surface and reconstructing the bulk band topology. Our data reveal that bulk information can be detected because states at the edge of the surface-projected bulk band have a predominant role on the scattering patterns. With the aid of density functional calculations, we associate this effect with an intrinsic increase in the projected density of states of edge states. This enhancement is characteristic of the three-dimensional bulk band curvature, a phenomenon analog to a van Hove singularity. DOI: 10.1103/PhysRevLett.96.046801 PACS numbers: 73.20.At, 68.37.Ef, 71.20.ÿb The capabilities of the scanning tunneling microscope go far beyond imaging surfaces with atomic resolution by being able to probe the surface electronic structure, and extensive use has been made of this feature [1]. On metal surfaces, the electron dynamics can be analyzed by studying the characteristic wave patterns appearing in the proximity of surface defects such as steps and impurities [2][3][4]. In a general picture, the wave patterns are interpreted as the screening response of a 2D electron gas to defects such as steps or impurities. The wave patterns can be energy resolved by measuring spatial maps of the differential conductance dI=dV, which reproduce to first approximation the (energy dependent) local density of states (LDOS). In this case, the characteristic wavelength extracted from the dI=dV oscillations can be easily related with the state's wave vector k by simply performing a Fourier transformation [5][6][7]. Standing electron waves have been extensively analyzed to locally resolve different surface states properties, such as electron dispersion [7,8], hot electron lifetimes [9,10], or confinement at small terraces [11].Bulk electronic states are also present at a metal surface, but their influence on the standing wave patterns and hence their detection by a surface probe is not immediately obvious [12 -14]. They are thought to vanish near the termination of the bulk. Moreover, their projection onto the surface leads to a continuum band of states, which will suppress any oscillatory behavior of the density of states in real space. Here, we demonstrate that bulk band states influence standing wave patterns observed in STM. Our results reveal that states at the projected band edge have an unexpected predominant role, giving rise to a net oscillatory component in the proximity of surface defects, and allowing the reconstruction of a bulk band topology in reciprocal space using the Fourier-transform -STM technique. Density functional calculations confirm that band-edge states are intrinsically enhanced due threedimensional curvature of the band in the bulk.For this study the (110) surface of a silver single crystal is most appropriate. This surface has projected bulk states around the ÿ point in all the unoccu...
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