23 research outputs found
Quantitative analysis on electric dipole energy in Rashba band splitting
We report on quantitative comparison between the electric dipole energy and the Rashba band splitting in model systems of Bi and Sb triangular monolayers under a perpendicular electric field. We used both first-principles and tight binding calculations on p-orbitals with spin-orbit coupling. First-principles calculation shows Rashba band splitting in both systems. It also shows asymmetric charge distributions in the Rashba split bands which are induced by the orbital angular momentum. We calculated the electric dipole energies from coupling of the asymmetric charge distribution and external electric field, and compared it to the Rashba splitting. Remarkably, the total split energy is found to come mostly from the difference in the electric dipole energy for both Bi and Sb systems. A perturbative approach for long wave length limit starting from tight binding calculation also supports that the Rashba band splitting originates mostly from the electric dipole energy difference in the strong atomic spin-orbit coupling regime.1131Ysciescopu
Experimental observation of hidden Berry curvature in inversion-symmetric bulk 2H-WSe2
We investigate the hidden Berry curvature in bulk 2H-WSe2 by utilizing the
surface sensitivity of angle resolved photoemission (ARPES). The symmetry in
the electronic structure of transition metal dichalcogenides is used to
uniquely determine the local orbital angular momentum (OAM) contribution to the
circular dichroism (CD) in ARPES. The extracted CD signals for the K and K'
valleys are almost identical but their signs, which should be determined by the
valley index, are opposite. In addition, the sign is found to be the same for
the two spin-split bands, indicating that it is independent of spin state.
These observed CD behaviors are what are expected from Berry curvature of a
monolayer of WSe2. In order to see if CD-ARPES is indeed representative of
hidden Berry curvature within a layer, we use tight binding analysis as well as
density functional calculation to calculate the Berry curvature and local OAM
of a monolayer WSe2. We find that measured CD-ARPES is approximately
proportional to the calculated Berry curvature as well as local OAM, further
supporting our interpretation.Comment: 6 pages, 3 figure
surface reconstruction and electronic structure of BaSnO film
We studied surface and electronic structures of barium stannate (BaSnO)
thin-film by low energy electron diffraction (LEED), and angle-resolved
photoemission spectroscopy (ARPES) techniques.
BaSnO/BaLaSnO/SrTiO (10 nm/100 nm/0.5 mm) samples
were grown using pulsed-laser deposition (PLD) method and were \emph{ex-situ}
transferred from PLD chamber to ultra-high vacuum (UHV) chambers for annealing,
LEED and ARPES studies. UHV annealing starting from 300C up to
550C, followed by LEED and ARPES measurements show 11
surfaces with non-dispersive energy-momentum bands. The 11 surface
reconstructs into a one at the annealing
temperature of 700C where the ARPES data shows clear dispersive bands
with valence band maximum located around 3.3 eV below Fermi level. While the
surface reconstruction is stable under
further UHV annealing, it is reversed to 11 surface by annealing the
sample in 400 mTorr oxygen at 600C. Another UHV annealing at
600C followed by LEED and ARPES measurements, suggests that LEED
surface reconstruction and ARPES
dispersive bands are reproduced. Our results provide a better picture of
electronic structure of BaSnO surface and are suggestive of role of oxygen
vacancies in the reversible surface
reconstruction.Comment: 7 pages, 4 figures, Journa
Understanding the Role of Electronic Effects in CO on the Pt-Sn Alloy Surface via Band Structure Measurements
Using angle-resolved photoemission spectroscopy, we show direct evidence for charge transfer between adsorbed molecules and metal substrates, i.e., chemisorption of CO on Pt(111) and Pt-Sn/Pt(111) 2 x 2 surfaces. The observed band structures show a unique signature of charge transfer as CO atoms are adsorbed, revealing the roles of specific orbital characters participating in the chemisorption process. As the coverage of CO increases, the degree of charge transfer between CO and Pt shows a clear difference to that of Pt-Sn. With comparison to density functional theory calculation results, the observed distinct features in the band structure are interpreted as back-donation bonding states formed between the Pt molecular orbital and the 2 pi orbital of CO. Furthermore, the change in the surface charge concentration, measured from the Fermi surface area, shows that the Pt surface has a larger charge concentration change than the Pt-Sn surface upon CO adsorption. The differences between Pt and Pt-Sn surfaces are due to the effect of Pt-Sn intermetallic bonding on the interaction of CO with the surface
dbHiMo : a web-based epigenomics platform for histone-modifying enzymes
Over the past two decades, epigenetics has evolved into a key concept for understanding regulation of gene expression. Among many epigenetic mechanisms, covalent modifications such as acetylation and methylation of lysine residues on core histones emerged as a major mechanism in epigenetic regulation. Here, we present the database for histone-modifying enzymes (dbHiMo; http://hme.riceblast.snu.ac.kr/) aimed at facilitating functional and comparative analysis of histone-modifying enzymes (HMEs). HMEs were identified by applying a search pipeline built upon profile hidden Markov model (HMM) to proteomes. The database incorporates 11 576 HMEs identified from 603 proteomes including 483 fungal, 32 plants and 51 metazoan species. The dbHiMo provides users with web-based personalized data browsing and analysis tools, supporting comparative and evolutionary genomics. With comprehensive data entries and associated web-based tools, our database will be a valuable resource for future epigenetics/epigenomics studies.Peer reviewe
Electronic structures of CO adsorbed Pt-skin surface on Pt–Co and Pt–Ni alloys
© 2021 Korean Physical SocietyBy using angle resolved photoemission spectroscopy, we investigate the electronic structures of Pt-skin layer of Pt–Co and Pt–Ni alloys with CO molecules on the surface. Measured Fermi surface maps and band dispersions reflect the signatures of chemical bonding between Pt-skin layer and CO molecules. Furthermore, the degree of chemical bonding strength of CO molecules, estimated from the energy shift of the participating bands, is found to be reduced on both Pt bimetallic alloys. Our results show how the surface band structure of Pt bimetallic alloys is modified with molecular orbitals of CO molecules on the surface, revealing the important role of the electronic structure in the determination of chemical properties of bimetallic alloys.11Nsciescopuskc
New perspective on giant Rahba effect
The giant Rashba splitting on Bi/Ag(111) alloy surface which is two order of amplitude larger than Rashba on Au(111)
surface has been reported from the experiment. [1] From the DFT calculations, it has been known that the amplitude
of the splitting depends on the distance between Bi and Ag on surface, but the reason for that is still obscure. [2]
Some proposals were made to explain the giant Rashba such as the role of in-plane potential gradient, very strong
surface electric field and spin-orbit coupling. [1,3,4] However, the origin of the giant Rashba splitting has not been
disclosed clearly and there must be unrevealed mechanism to explain it.
In this study based on DFT calculation, we would give a new perspective on giant Rashba effect.1