1,808 research outputs found
Complex Analysis of a Piece of Toda Lattice
We study a small piece of two dimensional Toda lattice as a complex dynamical
system. In particular the Julia set, which appears when the piece is deformed,
is shown analytically how it disappears as the system approaches to the
integrable limit.Comment: 17 pages, LaTe
Phase Change Observed in Ultrathin Ba0.5Sr0.5TiO3 Films by in-situ Resonant Photoemission Spectroscopy
Epitaxial Ba0.5Sr0.5TiO3 thin films were prepared on Nb-doped SrTiO3
(100)substrates by the pulsed laser deposition technique, and were studied by
measuring the Ti 2p - 3d resonant photoemission spectra in the valence-band
region as a function of film thickness, both at room temperature and low
temperature. Our results demonstrated an abrupt variation in the spectral
structures between 2.8 nm (~7 monolayers) and 2.0 nm (~5 monolayers)
Ba0.5Sr0.5TiO3 films, suggesting that there exists a critical thickness for
phase change in the range of 2.0 nm to 2.8 nm. This may be ascribed mainly to
the intrinsic size effects.Comment: 13 pages, 4 figure
Magnetic Phase Transition of the Perovskite-type Ti Oxides
Properties and mechanism of the magnetic phase transition of the
perovskite-type Ti oxides, which is driven by the Ti-O-Ti bond angle
distortion, are studied theoretically by using the effective spin and
pseudo-spin Hamiltonian with strong Coulomb repulsion. It is shown that the
A-type antiferromagnetic(AFM(A)) to ferromagnetic(FM) phase transition occurs
as the Ti-O-Ti bond angle is decreased. Through this phase transition, the
orbital state is hardly changed so that the spin-exchange coupling along the
c-axis changes nearly continuously from positive to negative and takes
approximately zero at the phase boundary. The resultant strong
two-dimensionality in the spin coupling causes a rapid suppression of the
critical temperature as is observed experimentally.Comment: 9 pages, 5 figure
Room temperature and low-field resonant enhancement of spin Seebeck effect in partially compensated magnets
Resonant enhancement of spin Seebeck effect (SSE) due to phonons was recently
discovered in Y3Fe5O12 (YIG). This effect is explained by hybridization between
the magnon and phonon dispersions. However, this effect was observed at low
temperatures and high magnetic fields, limiting the scope for applications.
Here we report observation of phonon-resonant enhancement of SSE at room
temperature and low magnetic field. We observed in Lu2BiFe4GaO12 and
enhancement 700 % greater than that in a YIG film and at very low magnetic
fields around 10-1 T, almost one order of magnitude lower than that of YIG. The
result can be explained by the change in the magnon dispersion induced by
magnetic compensation due to the presence of non-magnetic ion substitutions.
Our study provides a way to tune the magnon response in a crystal by chemical
doping with potential applications for spintronic devices.Comment: 17 pages, 4 figure
Cyclotron resonance of correlated electrons in semiconductor heterostructures
The cyclotron resonance absorption of two-dimensional electrons in
semiconductor heterostructures in high magnetic fields is investigated. It is
assumed that the ionized impurity potential is a dominant scattering mechanism,
and the theory explicitly takes the Coulomb correlation effect into account
through the Wigner phonons. The cyclotron resonance linewidth is in
quantitative agreement with the experiment in the Wigner crystal regime at
T=4.2K. Similar to the cyclotron resonance theory of the charge density waves
pinned by short-range impurities, the present results for the long-range
scattering also show the doubling of the resonance peaks. However, unlike the
case of the charge density waves, our theory gives the pinning mode independent
of the bulk compressibility of the substrate materials.Comment: 6 pages, 5 figure
Soft x-ray magnetic circular dichroism study of weakly ferromagnetic ZnVO thin film
We performed a soft x-ray magnetic circular dichroism (XMCD) study of a
ZnVO thin film which showed small ferromagnetic moment. Field and
temperature dependences of V 2 XMCD signals indicated the coexistence of
Curie-Weiss paramagnetic, antiferromagnetic, and possibly ferromagnetic V ions,
quantitatively consistent with the magnetization measurements. We attribute the
paramagnetic signal to V ions substituting Zn sites which are somewhat
elongated along the c-axis
Fermi Surface of 3d^1 Perovskite CaVO3 Near the Mott Transition
We present a detailed de Haas van Alphen effect study of the perovskite
CaVO3, offering an unprecedented test of electronic structure calculations in a
3d transition metal oxide. Our experimental and calculated Fermi surfaces are
in good agreement -- but only if we ignore large orthorhombic distortions of
the cubic perovskite structure. Subtle discrepancies may shed light on an
apparent conflict between the low energy properties of CaVO3, which are those
of a simple metal, and high energy probes which reveal strong correlations that
place CaVO3 on the verge of a metal-insulator transition.Comment: 4 pages, 4 figures (REVTeX
Dual Resonance Model Solves the Yang-Baxter Equation
The duality of dual resonance models is shown to imply that the four point
string correlation function solves the Yang-Baxter equation. A reduction of
transfer matrices to symmetry is described by a restriction of the KP
function to Toda molecules.Comment: 10 pages, LaTe
Lowering and raising operators for the free Meixner class of orthogonal polynomials
We compare some properties of the lowering and raising operators for the
classical and free classes of Meixner polynomials on the real line
Indication of antiferromagnetic interaction between paramagnetic Co ions in the diluted magnetic semiconductor ZnCoO
The magnetic properties of ZnCoO ( and 0.10) thin films,
which were homo-epitaxially grown on a ZnO(0001) substrates with varying
relatively high oxygen pressure, have been investigated using x-ray magnetic
circular dichroism (XMCD) at Co core-level absorption edge. The line
shapes of the absorption spectra are the same in all the films and indicate
that the Co ions substitute for the Zn sites. The magnetic-field and
temperature dependences of the XMCD intensity are consistent with the
magnetization measurements, indicating that except for Co there are no
additional sources for the magnetic moment, and demonstrate the coexistence of
paramagnetic and ferromagnetic components in the homo-epitaxial
ZnCoO thin films, in contrast to the ferromagnetism in the
hetero-epitaxial ZnCoO films studied previously. The analysis of
the XMCD intensities using the Curie-Weiss law reveals the presence of
antiferromagnetic interaction between the paramagnetic Co ions. Missing XMCD
intensities and magnetization signals indicate that most of Co ions are
non-magnetic probably because they are strongly coupled antiferromagnetically
with each other. Annealing in a high vacuum reduces both the paramagnetic and
ferromagnetic signals. We attribute the reductions to thermal diffusion and
aggregation of Co ions with antiferromagnetic nanoclusters in
ZnCoO.Comment: 21 pages, 7 figures, accepted for Physical Review
- …