23,066 research outputs found
Pre-K-Edge Structure on Anomalous X-Ray Scattering in LaMnO3
We study the pre-K-edge structure of the resonant X-ray scattering for
forbidden reflections (anomalous scattering) in LaMnO3, using the band
calculation based on the local density approximation. We find a two-peak
structure with an intensity approximately 1/100 of that of the main peak. This
originates from a mixing of 4p states of Mn to 3d states of neighboring Mn
sites. The effect is enhanced by an interference with the tail of the main
peak. The effect of the quadrupole transition is found to be one order of
magnitude smaller than that of the dipole transition, modifying slightly the
azimuthal-angle dependence.Comment: 4 pages, 5 figures, submitted to J. Phys. Soc. Jp
Thermoelectric transport of perfectly conducting channels in two- and three-dimensional topological insulators
Topological insulators have gapless edge/surface states with novel transport
properties. Among these, there are two classes of perfectly conducting channels
which are free from backscattering: the edge states of two-dimensional
topological insulators and the one-dimensional states localized on dislocations
of certain three-dimensional topological insulators. We show how these novel
states affect thermoelectric properties of the systems and discuss
possibilities to improve the thermoelectric figure of merit using these
materials with perfectly conducting channels.Comment: 10 pages, 6 figures, proceedings for The 19th International
Conference on the Application of High Magnetic Fields in Semiconductor
Physics and Nanotechnology (HMF-19
Single-dopant resonance in a single-electron transistor
Single dopants in semiconductor nanostructures have been studied in great
details recently as they are good candidates for quantum bits, provided they
are coupled to a detector. Here we report coupling of a single As donor atom to
a single-electron transistor (SET) in a silicon nanowire field-effect
transistor. Both capacitive and tunnel coupling are achieved, the latter
resulting in a dramatic increase of the conductance through the SET, by up to
one order of magnitude. The experimental results are well explained by the rate
equations theory developed in parallel with the experiment.Comment: 16 pages, 8 figure
RESONANT BANDWIDTH ESTIMATION OF VOWELS USING CLUSTERED-LINE SPECTRUM MODELING FOR PRESSURE SPEECH WAVEFORMS
Mechanism of carrier-induced ferromagnetism in magnetic semiconductors
Taking into account both random impurity distribution and thermal
fluctuations of localized spins, we have performed a model calculation for the
carrier (hole) state in GaMnAs by using the coherent potential
approximation (CPA). The result reveals that a {\it p}-hole in the band tail of
GaMnAs is not like a free carrier but is rather virtually bounded
to impurity sites. The carrier spin strongly couples to the localized {\it d}
spins on Mn ions. The hopping of the carrier among Mn sites causes the
ferromagnetic ordering of the localized spins through the double-exchange
mechanism. The Curie temperature obtained by using conventional parameters
agrees well with the experimental result.Comment: 7 pages, 4 figure
Magnetic susceptibility and low-temperature specific-heat of integrable 1-D Hubbard model under open-boundary conditions
The magnetic susceptibility and the low-temperature specific heat of the
1-dimensional Hubbard model under the integrable open-boundary conditions are
discussed through the Bethe ansatz with the string hypothesis. The
contributions of the boundary fields to both the susceptibility and the
specific heat are obtained, and their exact expressions are analytically
derived.Comment: 14 pages, Latex, No figures, to appear in J. Phys. A: Gen. & Mat
Critical properties and R\'enyi entropies of the spin-3/2 XXZ chain
We discuss entanglement and critical properties of the spin-3/2 XXZ chain in
its entire gapless region. Employing density-matrix renormalization group
calculations combined with different methods based on level spectroscopy,
correlation functions and entanglement entropies, we determine the sound
velocity and the Luttinger parameter of the model as a function of the
anisotropy parameter. Then, we focus on entanglement properties by
systematically studying the behavior of R\'enyi entropies under both open and
periodic boundary conditions, providing further evidence of recent findings
about entanglement entropies of excited states in conformal field theory.Comment: 8 pages, 10 figures; small text revisions and a new figure. Accepted
for publication in Phys. Rev.
Resonant X-Ray Scattering from CeB
We calculate the resonant x-ray scattering (RXS) spectra near the Ce absorption edge in CeB, on the basis of a microscopic model that the
states of Ce are atomic while the states form an energy band with a
reasonable density of states. In the initial state, we employ an effective
Hamiltonian of Shiina {\it et al}. in the antiferro-quadrupole (AFQ) ordering
phase, while we construct the wave function consistent with the neutron
scattering experiment in the magnetic ground state. In the intermediate state,
we take full account of the intra-atomic Coulomb interaction. Without assuming
any lattice distortion, we obtain sufficient RXS intensities on the AFQ
superlattice spot. We obtain the spectral shape, the temperature and magnetic
field dependences in good agreement with the experiment, thus demonstrating the
mechanism that the intensity is brought about by the modulation of states
through the anisotropic term of the - Coulomb interaction. In the
magnetic ground state, a small pre-edge peak is found by the process. On
the magnetic superlattice spot, we get a finite but considerably small
intensity. The magnetic form factor is briefly discussed.Comment: Latex, 10 pages, 12 figures. To be published in J. Phys. Soc. Jpn.,
Vol.71, No. 7 (2002
Nonlinear Integral Equations for Thermodynamics of the U_{q}(\hat{sl(r+1)}) Perk-Schultz Model
We propose a system of nonlinear integral equations (NLIE) which describes
the thermodynamics of the U_{q}(\hat{sl(r+1)}) Perk-Schultz model. These NLIE
correspond to a trigonometric analogue of our previous result
(cond-mat/0212280), and contain only r unknown functions. In particular, they
reduce to Takahashi's NLIE for the XXZ spin chain (cond-mat/0010486) if r=1. We
also calculate the high temperature expansion of the free energy. In particular
for r=1 case, we have succeeded to derive the coefficients of order
O((\frac{J}{T})^{99}).Comment: 19 pages, 4 figures, only the Mathematica file for the high
temperature expansion is replaced, to appear in J.Phys.Soc.Jpn.Vol.74 No.3
(2005
First-order transition between a small-gap semiconductor and a ferromagnetic metal in the isoelectronic alloys FeSiGe
The contrasting groundstates of isoelectronic and isostructural FeSi and FeGe
can be explained within an extended local density approximation scheme (LDA+U)
by an appropriate choice of the onsite Coulomb repulsion, on the Fe-sites.
A minimal two-band model with interband interactions allows us to obtain a
phase diagram for the alloys FeSiGe. Treating the model in a mean
field approximation, gives a first order transition between a small-gap
semiconductor and a ferromagnetic metal as a function of magnetic field,
temperature, and concentration, . Unusually the transition from metal to
insulator is driven by broadening, not narrowing, the bands and it is the
metallic state that shows magnetic order.Comment: 4 pages, 5 figure
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