We performed angle-resolved photoemission experiments on Au(111) surface with circularly polarized light. Data were taken with photon energies in the range between 20 and 100 eV in order to investigate the photon energy dependent behavior in the circular dichroism (CD). While the magnitude of the normalized CD value varies with a maximum value of about 70%, the sign of CD does not change for the photon energy within the range, inconsistent with the prediction based on the density-functional theory (DFT) calculation. Our calculation of the CD using DFT initial state and free electron final state shows a better consistency with experimental results than an earlier study using the inverse low-energy electron diffraction state as the final state. We briefly discuss the dominating factor that determines the CD from Au (111) states.
We studied surface and electronic structures of barium stannate (BaSnO3) thin-film by low energy electron diffraction (LEED), and angle-resolved photoemission spectroscopy (ARPES) techniques. BaSnO3/Ba0.96La0.04SnO3/SrTiO3 (10 nm/100 nm/0.5 mm) samples were grown using pulsed-laser deposition (PLD) method and were ex-situ transferred from PLD chamber to ultra-high vacuum (UHV) chambers for annealing, LEED and ARPES studies. UHV annealing starting from 300 • C up to 550 • C, followed by LEED and ARPES measurements show 1×1 surfaces with non-dispersive energy-momentum bands. The 1×1 surface reconstructs into a √ 2× √ 2R45 • one at the annealing temperature of 700 • C where the ARPES data shows clear dispersive bands with valence band maximum located around 3.3 eV below Fermi level. While the √ 2× √ 2R45 • surface reconstruction is stable under further UHV annealing, it is reversed to 1×1 surface by annealing the sample in 400 mTorr oxygen at 600 • C. Another UHV annealing at 600 • C followed by LEED and ARPES measurements, suggests that LEED √ 2× √ 2R45 • surface reconstruction and ARPES dispersive bands are reproduced. Our results provide a better picture of electronic structure of BaSnO3 surface and are suggestive of role of oxygen vacancies in the reversible √ 2× √ 2R45 • surface reconstruction.
We have performed angle resolved photoemission spectroscopy (ARPES) experiments on the surface states of SrTiO3(001) using linearly and circularly polarized light to investigate the subband structures of out-of-plane d xz/yz orbitals and chiral orbital angular momentum (OAM). The data taken in the first Brillouin zone reveal new subbands for d xz/yz orbitals with Fermi wave vectors of 0.25 and 0.45Å −1 in addition to the previously reported ones. As a result, there are at least two subbands for all the Ti 3d t2g orbitals. Our circular dichroism ARPES data is suggestive of a chiral OAM structure in the surface states and may provide clues to the origin of the linear Rashba-like surface band splitting.
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