Method of forming time-reversed LEED states from repeated-slab calculations.

A method of forming time-reversed low-energy electron diffraction (LEED) states using results of repeated-slab calculations is presented. The time-reversed LEED states are used in calculations of the matrix elements of photoelectron spectroscopy. The method is applied to spin- and angle-resolved photoelectron spectroscopy of the Bi(111) surface. Calculations are performed for excitation from surface states by linearly polarized light. Calculated results reproduce spin average values measured as a function of polarization angle of light and explain the intensity asymmetry experimentally observed. Calculations for excitation by circularly polarized light are also performed, and relations of spin expectation values between linear and circularly polarized lights are discussed for systems with mirror symmetry.

Spin-dependent quantum interference in photoemission process from spin-orbit coupled states.

Spin-orbit interaction entangles the orbitals with the different spins. The spin-orbital-entangled states were discovered in surface states of topological insulators. However, the spin-orbital-entanglement is not specialized in the topological surface states. Here, we show the spin-orbital texture in a surface state of Bi(111) by laser-based spin- and angle-resolved photoelectron spectroscopy (laser-SARPES) and describe three-dimensional spin-rotation effect in photoemission resulting from spin-dependent quantum interference. Our model reveals that, in the spin-orbit-coupled systems, the spins pointing to the mutually opposite directions are independently locked to the orbital symmetries. Furthermore, direct detection of coherent spin phenomena by laser-SARPES enables us to clarify the phase of the dipole transition matrix element responsible for the spin direction in photoexcited states. These results permit the tuning of the spin polarization of optically excited electrons in solids with strong spin-orbit interaction.

Electron-phonon interaction and localization of surface-state carriers in a metallic monolayer.

Temperature-dependent electron transport in a metallic surface superstructure, Si(111)sqrt[3] x sqrt[3]-Ag, was studied by a micro-four-point probe method and photoemission spectroscopy. The surface-state conductivity exhibits a sharp transition from metallic conduction to strong localization at approximately 150 K. The metallic regime is due to electron-phonon interaction while the localization seemingly originates from coherency of electron waves. Random potential variations, caused by Friedel oscillations of surface electrons around defects, likely induce strong carrier localization.