133 research outputs found
Anomalous momentum dependence of the multiband electronic structure of FeSe_1-xTe_x superconductors induced by atomic disorder
When periodicity of crystal is disturbed by atomic disorder, its electronic
state becomes inhomogeneous and band dispersion is obscured. In case of
Fe-based superconductors, disorder of chalcogen/pnictogen height causes
disorder of Fe 3d level splitting. Here, we report an angle-resolved
photoemission spectroscopy study on FeSe_1-xTe_x with the chalcogen height
disorder, showing that the disorder affects the Fe 3d band dispersions in an
orbital-selective way instead of simple obscuring effect. The reverse of the Fe
3d level splitting due to the chalcogen height difference causes the splitting
of the hole band with Fe 3d x^2-y^2 character around the Gamma point.Comment: 5 pages, 4 figure
Core-to-Rydberg band shift and broadening of hydrogen bonded ammonia clusters studied with nitrogen K-edge excitation spectroscopy
Nitrogen 1s (N 1s) core-to-Rydberg excitation spectra of hydrogen-bonded clusters of ammonia (AM) have been studied in the small cluster regime of beam conditions with time-of-flight (TOF) fragmentmass spectroscopy. By monitoring partial-ion-yield spectra of cluster-origin products, "cluster" specific excitation spectra could be recorded. Comparison of the "cluster" band with "monomer" band revealed that the first resonance bands of clusters corresponding to N 1s -> 3sa(1)/3pe of AM monomer are considerably broadened. The changes of the experimental core-to-Rydberg transitions Delta FWHM (N 1s -> 3sa(1)/3pe) = similar to 0.20/similar to 0.50 eV compare well with the x ray absorption spectra of the clusters generated by using density functional theory (DFT) calculation. The broadening of the core-to-Rydberg bands in small clusters is interpreted as being primarily due to the splitting of non-equivalent core-hole N 1s states caused by both electrostatic core-hole and hydrogen-bonding (H(3)N center dot center dot center dot H-NH(2)) interactions upon dimerization. Under Cs dimer configuration, core-electron binding energy of H-N (H-donor) is significantly decreased by the intermolecular core-hole interaction and causes notable redshifts of core-excitation energies, whereas that of lone-pair nitrogen (H-acceptor) is slightly increased and results in appreciable blueshifts in the core-excitation bands. The result of the hydrogen-bonding interaction strongly appears in the n-sigma* orbital correlation, destabilizing H-N donor Rydberg states in the direction opposite to the core-hole interaction, when excited N atom with H-N donor configuration strongly possesses the Rydberg component of anti-bonding sigma* (N-H) character. Contributions of other cyclic H-bonded clusters (AM)(n) with n >= 3 to the spectral changes of the N 1s -> 3sa(1)/3pe bands are also examined. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3673778
Sheet Dependence on Superconducting Gap in Oxygen-Deficient Iron-based Oxypnictide Superconductors NdFeAs0.85
Photoemission spectroscopy with low-energy tunable photons on
oxygen-deficient iron-based oxypnictide superconductors NdFeAsO0.85 (Tc=52K)
reveals a distinct photon-energy dependence of the electronic structure near
the Fermi level (EF). A clear shift of the leading-edge can be observed in the
superconducting states with 9.5 eV photons, while a clear Fermi cutoff with
little leading-edge shift can be observed with 6.0 eV photons. The results are
indicative of the superconducting gap opening not on the hole-like ones around
Gamma (0,0) point but on the electron-like sheets around M(pi,pi) point.Comment: 8 pages, 3 figure
Chiral orbital-angular-momentum in the surface states of Bi2Se3
Locking of the spin of a quasi-particle to its momentum in split bands of on
the surfaces of metals and topological insulators (TIs) is understood in terms
of Rashba effect where a free electron in the surface states feels an effective
magnetic field. On the other hand, the orbital part of the angular momentum
(OAM) is usually neglected. We performed angle resolved photoemission
experiments with circularly polarized lights and first principles density
functional calculation with spin-orbit coupling on a TI, Bi2Se3, to study the
local OAM of the surface states. We show from the results that OAM in the
surface states of Bi2Se3 is significant and locked to the electron momentum in
opposite direction to the spin, forming chiral OAM states. Our finding opens a
new possibility to have strong light-induced spin-polarized current in the
surface states.Comment: 5 pages, 4 figures, 1 tabl
High-Energy Anomaly in the Band Dispersion of the Ruthenate Superconductor
We reveal a “high-energy anomaly" (HEA) in the band dispersion of the unconventional ruthenate superconductor Sr2RuO4, by means of high-resolution angle-resolved photoemission spectroscopy (ARPES) with tunable energy and polarization of incident photons. This observation provides another class of correlated materials exhibiting this anomaly beyond high-Tc cuprates. We demonstrate that two distinct types of band renormalization associated with and without the HEA occur as a natural consequence of the energetics in the bandwidth and the energy scale of the HEA. Our results are well reproduced by a simple analytical form of the self-energy based on the Fermi-liquid theory, indicating that the HEA exists at a characteristic energy scale of the multielectron excitations. We propose that the HEA universally emerges if the systems have such a characteristic energy scale inside of the bandwidth
Observation of a Highly Spin Polarized Topological Surface State in GeBiTe
Spin polarization of a topological surface state for GeBiTe, the
newly discovered three-dimensional topological insulator, has been studied by
means of the state of the art spin- and angle-resolved photoemission
spectroscopy. It has been revealed that the disorder in the crystal has a minor
effect on the surface state spin polarization and it exceeds 75% near the Dirac
point in the bulk energy gap region (180 meV). This new finding for
GeBiTe promises not only to realize a highly spin polarized surface
isolated transport but to add new functionality to its thermoelectric and
thermomagnetic properties.Comment: 5 pages, 4 figure
Electronic structure of Fe1.04(Te0.66Se0.34)
We report the electronic structure of the iron-chalcogenide superconductor,
Fe1.04(Te0.66Se0.34), obtained with high resolution angle-resolved
photoemission spectroscopy and density functional calculations. In
photoemission measurements, various photon energies and polarizations are
exploited to study the Fermi surface topology and symmetry properties of the
bands. The measured band structure and their symmetry characters qualitatively
agree with our density function theory calculations of Fe(Te0.66Se0.34),
although the band structure is renormalized by about a factor of three. We find
that the electronic structures of this iron-chalcogenides and the
iron-pnictides have many aspects in common, however, significant differences
exist near the Gamma-point. For Fe1.04(Te0.66Se0.34), there are clearly
separated three bands with distinct even or odd symmetry that cross the Fermi
energy (EF) near the zone center, which contribute to three hole-like Fermi
surfaces. Especially, both experiments and calculations show a hole-like
elliptical Fermi surface at the zone center. Moreover, no sign of spin density
wave was observed in the electronic structure and susceptibility measurements
of this compound.Comment: 7 pages, 9 figures. submitted to PRB on November 15, 2009, and
accepted on January 6, 201
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