2,018 research outputs found
Robust surface electronic properties of topological insulators: Bi2Te3 films grown by molecular beam epitaxy
The surface electronic properties of the important topological insulator
Bi2Te3 are shown to be robust under an extended surface preparation procedure
which includes exposure to atmosphere and subsequent cleaning and
recrystallization by an optimized in-situ sputter-anneal procedure under ultra
high vacuum conditions. Clear Dirac-cone features are displayed in
high-resolution angle-resolved photoemission spectra from the resulting
samples, indicating remarkable insensitivity of the topological surface state
to cleaning-induced surface roughness.Comment: 3 pages, 3 figure
Tomonaga-Luttinger Liquid in a Quasi-One-Dimensional S=1 Antiferromagnet Observed by the Specific Heat
Specific heat experiments on single crystals of the S=1 quasi-one-dimensional
bond-alternating antiferromagnet Ni(C_9H_24N_4)(NO_2)ClO_4, alias NTENP, have
been performed in magnetic fields applied both parallel and perpendicular to
the spin chains. We have found for the parallel field configuration that the
magnetic specific heat (C_mag) is proportional to temperature (T) above a
critical field H_c, at which the energy gap vanishes, in a temperature region
above that of the long-range ordered state. The ratio C_mag/T increases as the
magnetic field approaches H_c from above. The data are in good quantitative
agreement with the prediction of the c=1 conformal field theory in conjunction
with the velocity of the excitations calculated by a numerical diagonalization,
providing a conclusive evidence for a Tomonaga-Luttinger liquid.Comment: 4 pages, 4 postscript figure
Supersolid state in fermionic optical lattice systems
We study ultracold fermionic atoms trapped in an optical lattice with
harmonic confinement by combining the real-space dynamical mean-field theory
with a two-site impurity solver. By calculating the local particle density and
the pair potential in the systems with different clusters, we discuss the
stability of a supersolid state, where an s-wave superfluid coexists with a
density-wave state of checkerboard pattern. It is clarified that a confining
potential plays an essential role in stabilizing the supersolid state. The
phase diagrams are obtained for several effective particle densities.Comment: 7 pages, 5 figures, Phys. Rev. A in pres
Possible Kondo resonance in PrFe4P12 studied by bulk-sensitive photoemission
Pr 4f electronic states in Pr-based filled skutterudites PrT4X12(T=Fe and Ru;
X=P and Sb) have been studied by high-resolution bulk-sensitive Pr 3d-4f
resonance photoemission. A very strong spectral intensity is observed just
below the Fermi level in the heavy-fermion system PrFe4P12. The increase of its
intensity at lower temperatures is observed. We speculate that this is the
Kondo resonance of Pr, the origin of which is attributed to the strong
hybridization between the Pr 4f and the conduction electrons.Comment: 4 pages(camera ready format), 4 figures, ReVTeX
Electronic structures of CrX (X=S, Te) studied by Cr 2p soft x-ray magnetic circular dichroism
Cr 2p core excited XAS and XMCD spectra of ferromagnetic CrTe
with several concentrations of =0.11-0.33 and ferrimagnetic
CrS have been measured. The observed XMCD lineshapes are found to
very weakly depend on for CrTe. The experimental results
are analyzed by means of a configuration-interaction cluster model calculation
with consideration of hybridization and electron correlation effects. The
obtained values of the spin magnetic moment by the cluster model analyses are
in agreement with the results of the band structure calculation.The calculated
result shows that the doped holes created by the Cr deficiency exist mainly in
the Te 5porbital of CrTe, whereas the holes are likely to be in Cr
3d state for CrS.Comment: 8 pages, 6 figures, accepted for publication in Physical Review
Kink far below the Fermi level reveals new electron-magnon scattering channel in Fe
Many properties of real materials can be modeled using ab initio methods
within a single-particle picture. However, for an accurate theoretical
treatment of excited states, it is necessary to describe electron-electron
correlations including interactions with bosons: phonons, plasmons, or magnons.
In this work, by comparing spin- and momentum-resolved photoemission
spectroscopy measurements to many-body calculations carried out with a newly
developed first-principles method, we show that a kink in the electronic band
dispersion of a ferromagnetic material can occur at much deeper binding
energies than expected (E_b=1.5 eV). We demonstrate that the observed spectral
signature reflects the formation of a many-body state that includes a photohole
bound to a coherent superposition of renormalized spin-flip excitations. The
existence of such a many-body state sheds new light on the physics of the
electron-magnon interaction which is essential in fields such as spintronics
and Fe-based superconductivity.Comment: 6 pages, 2 figure
Incommensurate state in a quasi-one-dimensional bond-alternating antiferromagnet with frustration in magnetic fields
We investigate the critical properties of the bond-alternating spin
chain with a next-nearest-neighbor interaction in magnetic fields. By the
numerical calculation and the exact solution based on the effective
Hamiltonian, we show that there is a parameter region where the longitudinal
incommensurate spin correlation becomes dominant around the half-magnetization
of the saturation. Possible interpretations of our results are discussed. We
next investigate the effects of the interchain interaction (). The
staggered susceptibility and the uniform magnetization are calculated by
combining the density-matrix renormalization group method with the interchain
mean-field theory. For the parameters where the dominant longitudinal
incommensurate spin correlation appears in the case , the
staggered long-range order does not emerge up to a certain critical value of
around the half-magnetization of the saturation. We calculate the
static structure factor in such a parameter region. The size dependence of the
static structure factor at implies that the system has a
tendency to form an incommensurate long-range order around the
half-magnetization of the saturation. We discuss the recent experimental
results for the NMR relaxation rate in magnetic fields performed for
pentafluorophenyl nitronyl nitroxide.Comment: 10 pages, 12 figures, final version, to appear in PRB vol. 70, No. 5
(2004
Direct k-space mapping of the electronic structure in an oxide-oxide interface
The interface between LaAlO3 and SrTiO3 hosts a two-dimensional electron
system of itinerant carriers, although both oxides are band insulators.
Interface ferromagnetism coexisting with superconductivity has been found and
attributed to local moments. Experimentally, it has been established that Ti 3d
electrons are confined to the interface. Using soft x-ray angle-resolved
resonant photoelectron spectroscopy we have directly mapped the interface
states in k-space. Our data demonstrate a charge dichotomy. A mobile fraction
contributes to Fermi surface sheets, whereas a localized portion at higher
binding energies is tentatively attributed to electrons trapped by O-vacancies
in the SrTiO3. While photovoltage effects in the polar LaAlO3 layers cannot be
excluded, the apparent absence of surface-related Fermi surface sheets could
also be fully reconciled in a recently proposed electronic reconstruction
picture where the built-in potential in the LaAlO3 is compensated by surface
O-vacancies serving also as charge reservoir.Comment: 8 pages, 6 figures, incl. Supplemental Informatio
High-Temperature Transport Properties of Yb4−xSmxSb3
Polycrystalline L4Sb3 (L = La, Ce, Sm, and Yb) and Yb4−x Sm x Sb3, which crystallizes in the anti-Th3P4 structure type (I-43d no. 220), were synthesized via high-temperature reaction. Structural and chemical characterization were performed by x-ray diffraction and electronic microscopy with energy-dispersive x-ray analysis. Pucks were densified by spark plasma sintering. Transport property measurements showed that these compounds are n-type with low Seebeck coefficients, except for Yb4Sb3, which shows semimetallic behavior with hole conduction above 523 K. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb4Sb3 up to 0.7 at 1273 K
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