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Register a new userMeasurement of electron wave functions and confining potentials via photoemission
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Added by
F. J. Garcia de Abajo
Publication date
2002
fields
Physics
and research's language is
English
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Wave functions and electron potentials of laterally-confined surface states are determined experimentally by means of photoemission from stepped Au(111) surfaces. Using an iterative formalism borrowed from x-ray diffraction, we retrieve the real-space wave functions from the Fourier transform of their momentum representations, whose absolute values in turn are directly measured by angle-resolved photoemission. The effective confining potential is then obtained by introducing the wave functions into Schroedingers equation.
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The Allen-Heine-Cardona theory allows us to calculate phonon-induced electron self-energies from first principles without resorting to the adiabatic approximation. However, this theory has not been able to account for the change of the electron wave function, which is crucial if interband energy differences are comparable to the phonon-induced electron self-energy as in temperature-driven topological transitions. Furthermore, for materials without inversion symmetry, even the existence of such topological transitions cannot be investigated using the Allen-Heine-Cardona theory. Here, we generalize this theory to the renormalization of both the electron energies and wave functions. Our theory can describe both the diagonal and off-diagonal components of the Debye-Waller self-energy in a simple, unified framework. For demonstration, we calculate the electron-phonon coupling contribution to the temperature-dependent band structure and hidden spin polarization of BiTlSe2 across a topological transition. These quantities can be directly measured. Our theory opens a door for studying temperature-induced topological phase transitions in materials both with and without inversion symmetry.
Quantum Monte Carlo simulations of interacting electrons in solids often use Slater-Jastrow trial wave functions with Jastrow factors containing one- and two-body terms. In uniform systems the long-range behavior of the two-body term may be deduced from the random-phase approximation (RPA) of Bohm and Pines. Here we generalize the RPA to nonuniform systems. This gives the long-range behavior of the inhomogeneous two-body correlation term and provides an accurate analytic expression for the one-body term. It also explains why Slater-Jastrow trial wave functions incorporating determinants of Hartree-Fock or density-functional orbitals are close to optimal even in the presence of an RPA Jastrow factor. After adjusting the inhomogeneous RPA Jastrow factor to incorporate the known short-range behavior, we test it using variational Monte Carlo calculations. We find that the most important aspect of the two-body term is the short-range behavior due to electron-electron scattering, although the long-range behavior described by the RPA should become more important at high densities.
Photoelectron emission microscopy PEEM is a powerful tool to spectroscopically image dynamic surface processes at the nanoscale but is traditionally limited to ultra high or moderate vacuum conditions. Here, we develop a novel grapheme capped multichannel array sample platform that extends the capabilities of photoelectron spectromicroscopy to routine liquid and atmospheric pressure studies with standard PEEM setups. Using this platform, we show that graphene has only a minor influence on the electronic structure of water in the first few layers and thus will allow for the examination of minimally perturbed aqueous phase interfacial dynamics. Analogous to microarray screening technology in biomedical research, our platform is highly suitable for applications in tandem with large-scale data mining, pattern recognition, and combinatorial methods for spectro temporal and spatiotemporal analyses at solid liquid interfaces. Using Bayesian linear unmixing algorithm, we were able to discriminate between different X-ray induced water radiolysis scenarios and observe a metastable wetting intermediate water layer during the late stages of bubble formationformation
Auger Photoelectron Coincidence Spectroscopy (APECS), in which the Auger spectra is measured in coincidence with the core level photoelectron, is capable of pulling difficult to observe low energy Auger peaks out of a large background due mostly to inelastically scattered valence band (VB) photoelectrons. However the APECS method alone cannot eliminate the background due to valence band photoemission processes in which the initial photon energy is shared by two or more electrons and one of the electrons is in the energy range of the core level photoemission peak. Here we describe an experimental method to determine the contributions from these background processes and apply this method in the case of Copper M3VV Auger spectrum obtained in coincidence with the 3p3/2 photoemission peak. A beam of 200 eV photons was incident on a Cu(100) sample and a series of coincidence measurements were performed using a spectrometer equipped with two cylindrical mirror analyzers (CMAs). One CMA was set at series of fixed energies that ranged between the energy of the core and the VB peaks. The other CMA was scanned over a range corresponding to electrons leaving the surface between 0eV and 70eV. The set of measured spectra were then fit to a parameterized function which was extrapolated to determine the background in the APECS spectra due to multi-electron and inelastic VB photoemission processes. The extrapolated background was subtracted from the APECS spectrum to obtain the spectrum of electrons emitted solely as the result of the Auger process. A comparison of the coincidence spectrum with the same spectrum with background removed shows that in the case of Cu M3VV the background due to the inelastic scattering of VB electrons is negligible in the region of the Auger peak but is more than half the total signal down in the low energy tail of the Auger peak.
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