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Munisa Nurmamat, E. E. Krasovskii,
K. Kuroda,
M. Ye,
K. Miyamoto,
M. Nakatake,
T. Okuda,
H. Namatame,
M. Taniguchi,
E. V. Chulkov,
K. A. Kokh,
O. E. Tereshchenko,
A. Kimura
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ABSTRACT: Bias voltage dependent scattering of the topological surface state is studied
by scanning tunneling microscopy/spectroscopy for a clean surface of the
topological insulator Bi$_2$Te$_2$Se. A strong warping of constant energy
contours in the unoccupied part of the spectrum is found to lead to a
spin-selective scattering. The topological surface state persists to higher
energies in the unoccupied range far beyond the Dirac point, where it coexists
with the bulk conduction band. This finding sheds light on the spin and charge
dynamics over the wide energy range and opens a way to designing
opto-spintronic devices.
05/2013;
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ABSTRACT: We address the two-dimensional band-structure of graphene above the vacuum
level in the context of discrete states immersed in the three-dimensional
continuum. Scattering resonances are discovered that originate from the
coupling of the in-plane and perpendicular motions, as elucidated by the
analysis of an exactly solvable model. Some of the resonances turn into true
bound states at high-symmetry $\kv$ vectors. {\it Ab initio} scattering theory
verifies the existence of the resonances in realistic graphene and shows that
they lead to a total reflection of the incident electron below and total
transmission above the resonance energy.
07/2012;
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M. Ye,
S. V. Eremeev,
K. Kuroda, E. E. Krasovskii,
E. V. Chulkov,
Y. Takeda,
Y. Saitoh,
K. Okamoto,
S. Y. Zhu,
K. Miyamoto,
M. Arita,
M. Nakatake,
T. Okuda,
Y. Ueda,
K. Shimada,
H. Namatame,
M. Taniguchi,
A. Kimura
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ABSTRACT: Quasiparticle interference induced by cobalt adatoms on the surface of the topological insulator Bi2Se3 is studied by scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and x-ray magnetic circular dichroism. It is found that Co atoms are selectively adsorbed on top of Se sites and act as strong scatterers at the surface, generating anisotropic standing waves. A long-range magnetic order is found to be absent, and the surface state Dirac cone remains gapless. The anisotropy of the standing wave is ascribed to the heavily warped iso-energy contour of unoccupied states, where the scattering is allowed due to a nonzero out-of-plane spin.
Phys. Rev. B. 05/2012; 85(20).
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M. Ye,
S. V. Eremeev,
K Kuroda,
M. Nakatake,
S Kim,
Y Yamada, E. E. Krasovskii,
E. V. Chulkov,
M Arita,
H Miyahara,
T. Maegawa,
K Okamoto,
K Miyamoto,
T Okuda,
K Shimada,
H. Namatame,
M Taniguchi,
Y Ueda,
A Kimura
[show abstract]
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ABSTRACT: We studied the Ag-intercalated 3D topological insulator Bi$_{2}$Se$_{3}$ by
scanning tunneling microscopy/spectroscopy and angle-resolved photoemission
spectroscopy, combined with a first principles calculations. We demonstrate
that silver atoms deposited on the surface of Bi$_{2}$Se$_{3}$ are intercalated
between the quintuple layer (QL) units of the crystal, causing a expansion of
the van der Waals gaps and the detachment of topmost QLs from the bulk crystal.
This leads to a relocation (in the real space) of the the topological state
beneath the detached quintuple layers, accompanied by the emergence of
parabolic and "M-shaped" trivial bands localized above the relocated
topological states. These novel findings open a pathway to the engineering of
Dirac fermions shielded from the ambient contamination and may facilitate the
realization of fault-tolerant quantum devices.
12/2011;
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M. Ye,
S. V. Eremeev,
K Kuroda, E. E. Krasovskii,
E. V. Chulkov,
Y Takeda,
Y Saitoh,
K Okamoto,
S. Y. Zhu,
K Miyamoto,
M Arita,
M. Nakatake,
T Okuda,
Y Ueda,
K Shimada,
H. Namatame,
M Taniguchi,
A Kimura
[show abstract]
[hide abstract]
ABSTRACT: Quasiparticle interference induced by cobalt adatoms on the surface of the
topological insulator Bi$_{2}$Se$_{3}$ is studied by scanning tunneling
microscopy, angle-resolved photoemission spectroscopy and X-ray magnetic
circular dichroism. It is found that Co atoms are selectively adsorbed on top
of Se sites and act as strong scatterers at the surface, generating anisotropic
standing waves. A long-range magnetic order is found to be absent, and the
surface state Dirac cone remains gapless. The anisotropy of the standing wave
is ascribed to the heavily warped iso-energy contour of unoccupied states,
where the scattering is allowed due to a non-zero out-of-plane spin.
12/2011;
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K. Kuroda,
H. Miyahara,
M. Ye,
S. V. Eremeev,
Yu. M. Koroteev, E. E. Krasovskii,
E. V. Chulkov,
S. Hiramoto,
C. Moriyoshi,
Y. Kuroiwa,
K. Miyamoto,
T. Okuda,
M. Arita,
K. Shimada,
H. Namatame,
M. Taniguchi,
Y. Ueda,
A. Kimura
[show abstract]
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ABSTRACT: The first experimental evidence is presented of the topological insulator
state in PbBi$_{2}$Te$_{4}$. A single surface Dirac cone is observed by
angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation.
Topological invariants $\mathbb{Z}_2$ are calculated from the {\it ab initio}
band structure to be 1; (111). The observed two-dimensional iso-energy contours
in the bulk energy gap are found to be the largest among the known
three-dimensional topological insulators. This opens a pathway to achieving a
sufficiently large spin current density in future spintronic devices.
11/2011;
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Sunghun Kim,
M Ye,
K Kuroda,
Y Yamada, E E Krasovskii,
E V Chulkov,
K Miyamoto,
M Nakatake,
T Okuda,
Y Ueda,
K Shimada,
H Namatame,
M Taniguchi,
A Kimura
[show abstract]
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ABSTRACT: We have performed scanning tunneling microscopy and differential tunneling conductance (dI/dV) mapping for the surface of the three-dimensional topological insulator Bi(2)Se(3). The fast Fourier transformation applied to the dI/dV image shows an electron interference pattern near Dirac node despite the general belief that the backscattering is well suppressed in the bulk energy gap region. The comparison of the present experimental result with theoretical surface and bulk band structures shows that the electron interference occurs through the scattering between the surface states near the Dirac node and the bulk continuum states.
Physical Review Letters 07/2011; 107(5):056803. · 7.37 Impact Factor
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K Kuroda,
M Ye,
A Kimura,
S V Eremeev, E E Krasovskii,
E V Chulkov,
Y Ueda,
K Miyamoto,
T Okuda,
K Shimada,
H Namatame,
M Taniguchi
[show abstract]
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ABSTRACT: We report the first observation of a topological surface state on the (111) surface of the ternary chalcogenide TlBiSe₂ by angle-resolved photoemission spectroscopy. By tuning the synchrotron radiation energy we reveal that it features an almost ideal Dirac cone with the Dirac point well isolated from bulk continuum states. This suggests that TlBiSe₂ is a promising material for realizing quantum topological transport.
Physical Review Letters 10/2010; 105(14):146801. · 7.37 Impact Factor
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ABSTRACT: Nonlocal response of the surface to the incident light is included into an ab initio one-step photoemission theory. Surface-state normal emission spectra from Be(0001) and Al(100) are calculated by a full-potential scattering method and are found to agree well with the experiment in a wide energy range. The total exciting field is obtained within the random-phase approximation for jellium as well as for one-dimensional crystal models of the two surfaces. Material dependence of the multipole plasmon mode and strong effect of band structure on the photoyield is discussed.
Phys. Rev. B. 09/2010; 82(12).
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K Kuroda,
M Arita,
K Miyamoto,
M Ye,
J Jiang,
A Kimura, E E Krasovskii,
E V Chulkov,
H Iwasawa,
T Okuda,
K Shimada,
Y Ueda,
H Namatame,
M Taniguchi
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ABSTRACT: A hexagonal deformation of the Fermi surface of Bi2Se3 has been for the first time observed by angle-resolved photoemission spectroscopy. This is in contrast to the general belief that Bi2Se3 possesses an ideal Dirac cone. The hexagonal shape is found to disappear near the Dirac node, which would protect the surface state electrons from backscattering. It is also demonstrated that the Fermi energy of naturally electron-doped Bi2Se3 can be tuned by 1% Mg doping in order to realize the quantum topological transport.
Physical Review Letters 08/2010; 105(7):076802. · 7.37 Impact Factor
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A Kimura, E E Krasovskii,
R Nishimura,
K Miyamoto,
T Kadono,
K Kanomaru,
E V Chulkov,
G Bihlmayer,
K Shimada,
H Namatame,
M Taniguchi
[show abstract]
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ABSTRACT: Strong spin polarization of the photocurrent from bulk continuum states of Bi(111) is experimentally observed. On the basis of ab initio one-step photoemission theory the effect is shown to originate from the strong polarization of the initial states at the surface and to be the result of the surface sensitivity of photoemission. Final state effects cause deviations of the k{∥} dependence of polarization from strictly antisymmetric relative to Γ.
Physical Review Letters 08/2010; 105(7):076804. · 7.37 Impact Factor
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ABSTRACT: Photoelectron spectra from (100) and (111) surfaces of aluminum in the photon energy range 44–100 eV are measured and calculated within an ab initio one-step theory. Dispersion of spectral structures is interpreted in terms of unoccupied electronic structure of a semi-infinite crystal. The energy dependence of complex self-energy is derived from the experiment. The lifetimes of the (100) and (111) surface states and the photon energy dependence of the intensity of photoemission from the surface states are determined. A broad spectral structure is experimentally observed at the (111) surface, which disappears at the room temperature. It is tentatively interpreted as a surface resonance.
Phys. Rev. B. 10/2008; 78(16).
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ABSTRACT: Optical spectra of LaTiO3 are analyzed on the basis of an ab initio macroscopic dielectric function. The energy band structure and microscopic dielectric matrix are calculated with the extended linear augmented plane wave (ELAPW)-k · p method. The origin of UV spectral structures is elucidated. LaTiO3 is compared with SrTiO3 and BaTiO3 perovskites, and chemical trends in the formation of the UV reflectivity are discussed. The inclusion of local field corrections shifts spectral structures due to semi-core La 5p and Ti 3p excitations by several eV to higher energies. Calculated reflectivity and optical conductivity curves agree well with the experiment. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (b) 05/2006; 243(8):1885 - 1892. · 1.32 Impact Factor
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ABSTRACT: Electronic states of a material are intimately related to the dimension of the system. Epitaxial layers of transition metal dichalcogenides provide model systems in which the dimension can gradually be reduced by varying the film thickness. Applying combined angle-resolved photoemission and inverse photoemission on bulk HfS2 and epitaxial layers of HfS2 on WSe2, we investigate the influence of the film thickness on two- and three-dimensional valence and conduction band states. While the direct band gap is observed to be independent of the thickness, the dispersion of states interacting perpendicularly to the layers is strongly affected as found from normal emission spectra with varying photon energy. The latter, a decreasing band width with decreasing number of layers, may be expected from general physical arguments, whereas the former appears to be rather surprising. However, both is confirmed by ab initio extended linear augmented plane wave k⋅p band structure calculations.
Phys. Rev. B. 12/2003; 68(23).
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ABSTRACT: The optical properties of have been deduced using spectrophotometry and ellipsometry and calculated within the extended linear augmented plane wave framework in the energy range 0 - 6 eV. Good agreement amongst all approaches is obtained up to about 2 eV, beyond which there is some divergence between theory and experiment where, for reasons discussed, the theory needs further refinement.
Journal of Physics Condensed Matter 12/1998; 8(15):2549. · 2.55 Impact Factor
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ABSTRACT: Optical properties of ordered and disordered FeAl alloy films have been measured in the 0.5 - 5.0 eV energy range. The influence of the order - disorder structural transition on the optical properties of FeAl compounds has been studied. Experimental results for ordered FeAl are compared with the results of ab initio semi-relativistic extended linear augmented-plane-wave calculations, and explained in terms of the electronic energy band structures.
Journal of Physics Condensed Matter 12/1998; 9(50):11227. · 2.55 Impact Factor
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ABSTRACT: Optical properties of a trigonal polymorph of sulphur are explained in terms of the electronic energy band structure. The electron states of sulphur are obtained using the ab initio semi-relativistic extended linear augmented-plane-wave method (ELAPW). The density-of-states spectrum of the valence band is in agreement with x-ray photoemission, and x-ray emission spectra. The calculated polarized optical spectra are in satisfactory agreement with the experimental reflectivity spectra. All of the structures in the experimentally determined optical spectra in the energy region are interpreted in terms of interband transitions.
Journal of Physics Condensed Matter 12/1998; 10(18):4093. · 2.55 Impact Factor
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ABSTRACT: The optical and photoemission properties of RuO2 in the rutile structure have been examined, using the ab initio self-consistent energy-band structure. The semirelativistic extended linear augmented-plane-wave method was employed. Our calculated spectra of the anisotropic complex dielectric function (DF) agree well with experiment. The origin of the anisotropy of the experimentally observed structure in the DF spectra at ħω=1 eV has been elucidated. Comparison of the calculated ultraviolet photoemission spectrum for ħω=21 eV with experiment suggests that indirect transitions play an important role in formation of the spectrum.
Phys. Rev. B. 10/1995; 52(16).
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ABSTRACT: The electronic, optical, and conduction properties of the cetineites, a newly discovered class of crystalline nanoporous materials, have been calculated within a full-potential framework using the augmented Fourier components technique in combination with the extended linear augmented plane-wave k⋅p method. Photoemission, optical, and conductivity measurements have been performed and the calculated results are in conclusive agreement with all available experimental data. This helps in understanding the semiconducting nature of the cetineites, which is an exceptional property for nanoporous crystals.
Phys. Rev. B. 61(23).
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ABSTRACT: We report on a complete determination of the experimental and theoretical valence- and conduction-band structure of WSe2. The results of combined angle-resolved photoemission and inverse photoemission are discussed in the context of fully relativistic linear-muffin-tin-orbital and extended linear-augmented-plane-wave calculations. We measure an indirect band gap of 1.2 eV, and find the valence-band maximum to be located at the center of the Brillouin zone and the conduction-band minimum at 0.55ΓK.
Phys. Rev. B. 55(16).
