Electron-Lattice Interaction onα−Ga(010)

Abstract

We have investigated the (010) surface of a-Ga by angle-resolved photoemission and low energy electron diffraction. We find a surface state around theC point of the surface Brillouin zone. The electron-phonon coupling at this surface is very strong with an electron-phonon mass enhancement parameter of l 1.4 6 0.10. Our spectra show high background intensity in a projected bulk band gap which cannot be accounted for by defect scattering and is therefore interpreted as indicating a nonquasiparticle behavior. Upon cooling the sample below 220 K we observe a phase transition accompanied by spectral changes near the Fermi level. [S0031-9007(98)06909-9] PACS numbers: 73.20. At, 68.35.Rh, 71.38. + i, 71.45.Lr Semimetals such as beryllium or a-gallium have a low density of states at the Fermi level but their surfaces can support electronic states which cross E F and render the surface much more metallic than the bulk [1-3]. Hence, these surfaces form simple test cases for probing the properties of quasi-two-dimensional metals. The motivation for the work presented here is to study the effect of the electron-phonon coupling on the electronic structure of a two-dimensional metal. Although this effect is restricted to a small energy window around E F , it can be quite dramatic: In three dimensions it is predicted to lead to a nonquasiparticle behavior in the spectral function [4], an effect which has, to our knowledge, never been observed directly.The (010) surface of a-gallium is a very promising candidate for establishing an influence of the electron-phonon coupling on the dispersion of the electronic states. The size of the effect is given mainly by two factors: The phonon bandwidth E max sets the energy scale and the socalled electron-phonon mass enhancement parameter l describes the change in curvature of the dispersion at E F . Both are relatively high in bulk a-Ga (E max 40 meV [5] and l 0.98 [6]). A very important practical requirement for an investigation with angle-resolved photoemission is a geometrically flat surface because the small effect would otherwise be smeared out in momentum space. This seems to be fulfilled in the case of a-Ga͑010͒ as shown by the scanning tunneling microscopy (STM) results obtained by Züger and Dürig [7,8]. Finally, the surface has to support a surface state which crosses E F . Such a state was actually predicted for a-Ga͑010͒ in a recent first-principles calculation by Bernasconi, Chiarotti, and Tosatti (BCT) [3]. The state was found to form an electron pocket centered around the corner (theC point) of the surface Brillouin zone (SBZ) and to have a bandwidth of about 1.5 eV.Our a-gallium sample was cut mechanically from a bulk single crystal. The natural (010) surface was subsequently polished. Experiments were carried out in a UHV chamber on a toroidal grating monochromator beam line (TGM-4) at the Berlin synchrotron radiation source (BESSY). The chamber was equipped with a VG Instruments ADES400 spectrometer for angleresolved photoemission measurements, an Omicron LEED optics, a...

α-Ga(010) surface reconstruction: A LEED structural analysis of the(1×1)room temperature and(2Moré1, Soares2, Hove3 et al. 2003Phys. Rev. BSelf Cite91170View full textAdd to dashboardCite

“…9 The LEED patterns from the clean (1ϫ1) surface as well as from the reconstructed ͑LT͒ surface exhibited very sharp spots. Five I-V curves were taken, consisting of cumulative energy range of 790 eV.…”

“…11͒ and first-principles calculations. 12 Investigations of the ␣-Ga͑010͒ surface have revealed a reversible phase transition from the ͑1ϫ1͒ room temperature ͑RT͒ cell to a (2ͱ2ϫͱ2)R45°reconstruction at 232 K. 9,10 Later an additional splitting of the (Ϯ1/2,Ϯ1/2) spot was found with SPA-LEED. 11 It corresponds to a real-space periodicity of about 18 times the size of the unit cell.…”

“…Indeed, the surface melting temperature appears to be higher than its bulk counterpart. 7 The properties of this surface have been further investigated with x-ray diffraction, 8 Angle-resolved photoemission ͑ARUPS͒, 9,10 spot profile analysis ͑SPA͒ low-energy electron diffraction ͑LEED͒ ͑Ref. 11͒ and first-principles calculations.…”

Quantum Size Effects Induced Novel Properties in Two-Dimensional Electronic Systems: Pb Thin Films on Si(111)

“…Recently, prominent progress has been made in the study of the electron-phonon coupling strength () for the surface states in bulk materials [89][90][91] or for the QWS in thin films by ARPES. [92][93][94][95][96] For crystalline metal surfaces, the observed photoemission peak width is proportional to h " =, where is the lifetime of the hole state excitations.…”

The effect of reduced dimensionality on a semimetal: the electronic structure of the Bi(110) surface

“…Metallic surfaces have been found on Be [2,3] and α-Ga [4]. In both cases directional bonding is important and the bulk density of states has a minimum at the Fermi level, even though the absolute value is much higher than in a 'traditional' semimetal such as Sb, Bi or As.…”