2,646 research outputs found
Experimental band structure of the nearly half-metallic CuCrSe: An optical and magneto-optical study
Diagonal and off-diagonal optical conductivity spectra have been determined
form the measured reflectivity and magneto-optical Kerr effect (MOKE) over a
broad range of photon energy in the itinerant ferromagnetic phase of
CuCrSe at various temperatures down to T=10 K. Besides the low-energy
metallic contribution and the lower-lying charge transfer transition at
2 eV, a sharp and distinct optical transition was observed in the
mid-infrared region around 0.5 eV with huge magneto-optical activity.
This excitation is attributed to a parity allowed transition through the Se-Cr
hybridization-induced gap in the majority spin channel. The large off-diagonal
conductivity is explained by the high spin polarization in the vicinity of the
Fermi level and the strong spin-orbit interaction for the related charge
carriers. The results are discussed in connection with band structure
calculations
Asynchronous Graph Pattern Matching on Multiprocessor Systems
Pattern matching on large graphs is the foundation for a variety of
application domains. Strict latency requirements and continuously increasing
graph sizes demand the usage of highly parallel in-memory graph processing
engines that need to consider non-uniform memory access (NUMA) and concurrency
issues to scale up on modern multiprocessor systems. To tackle these aspects,
graph partitioning becomes increasingly important. Hence, we present a
technique to process graph pattern matching on NUMA systems in this paper. As a
scalable pattern matching processing infrastructure, we leverage a
data-oriented architecture that preserves data locality and minimizes
concurrency-related bottlenecks on NUMA systems. We show in detail, how graph
pattern matching can be asynchronously processed on a multiprocessor system.Comment: 14 Pages, Extended version for ADBIS 201
Spin-Gap Phase in the One-Dimensional t-J-J' Model
The spin-gap phase of the one-dimensional t-J-J' model is studied by the
level-crossing of the singlet and the triplet excitation spectra.
The phase boundary obtained between the Tomonaga-Luttinger and the spin-gap
phases is remarkably consistent with the analytical results at the
and the low-density limits discussed by Ogata et al.
The spin-gap phase has a single domain in the phase diagram even if the spin
gap opens at half-filling.
The phase boundary coincides with the line where the
Tomonaga-Luttinger liquid behaves as free electrons, in the low-density region.
The relation between our method and the solution of the two-electron problem
is also discussed.Comment: 4 pages(JPSJ.sty), 5 figures(EPS), to appear in J. Phys. Soc. Jpn.
67, No.3 (1998
Quantized Conductance of One-Dimensional Doped Mott Insulator
The possible modification of quantized conductance of one-dimensional doped
Mott insulator, where the Umklapp scattering plays an important role, is
studied based on the method by Maslov-Stone and Ponomarenko. At T=0 and away
from half-filling, the conductance is quantized as and there is no
renormalization by Umklapp scattering process. At finite temperatures, however,
the quantization is affected depending on the gate voltage and temperature.Comment: 10 pages, 4 figures, uses jpsj.st
Superconductivity emerging near quantum critical point of valence transition
The nature of the quantum valence transition is studied in the
one-dimensional periodic Anderson model with Coulomb repulsion between f and
conduction electrons by the density-matrix renormalization group method. It is
found that the first-order valence transition emerges with the quantum critical
point and the crossover from the Kondo to the mixed-valence states is strongly
stabilized by quantum fluctuation and electron correlation. It is found that
the superconducting correlation is developed in the Kondo regime near the sharp
valence increase. The origin of the superconductivity is ascribed to the
development of the coherent motion of electrons with enhanced valence
fluctuation, which results in the enhancement of the charge velocity, but not
of the charge compressibility. Statements on the valence transition in
connection with Ce metal and Ce compounds are given.Comment: 9 pages, 4 figure
Electronic states around a vortex core in high-Tc superconductors based on the t-J model
Electronic states around vortex cores in high-Tc superconductors are studied
using the two-dimensional t-J model in order to treat the d-wave
superconductivity with short coherence length and the antiferromagnetic (AF)
instability within the same framework. We focus on the disappearance of the
large zero-energy peak in the local density of states observed in high-Tc
superconductors. When the system is near the optimum doping, we find that the
local AF correlation develops inside the vortex cores. However, the detailed
doping dependence calculations confirm that the experimentally observed
reduction of the zero-energy peak is more reasonably attributed to the
smallness of the core size rather than to the AF correlation developed inside
the core. The correlation between the spatial dependence of the core states and
the core radius is discussed.Comment: 4 pages, 4 figure
Superconductivity in a Quasi One Dimensional Spin Liquid
The single rung t-J ladder is analyzed in a mean field theory using
Gutzwiller renormalization of the matrix elements to account for strong
correlation. The spin liquid (RVB) state at half-filling evolves into a
superconducting state upon doping. The order parameter has a modified d-wave
character. A lattice of weakly coupled ladders should show a superconducting
phase transition.Comment: 9 pages + 4 postscript files appende
NMR relaxation time around a vortex in stripe superconductors
Site-dependent NMR relaxation time is calculated in the vortex
state using the Bogoliubov-de Gennes theory, taking account of possible
"field-induced stripe'' states in which the magnetism arises locally around a
vortex core in d-wave superconductivity. The recently observed huge enhancement
below at a core site in TlBaCuO is
explained. The field-induced stripe picture explains consistently other
relevant STM and neutron experiments.Comment: 4 pages, 4 figure
Consistent alpha-cluster description of the 12C (0^+_2) resonance
The near-threshold 12C (0^+_2) resonance provides unique possibility for fast
helium burning in stars, as predicted by Hoyle to explain the observed
abundance of elements in the Universe. Properties of this resonance are
calculated within the framework of the alpha-cluster model whose two-body and
three-body effective potentials are tuned to describe the alpha - alpha
scattering data, the energies of the 0^+_1 and 0^+_2 states, and the
0^+_1-state root-mean-square radius. The extremely small width of the 0^+_2
state, the 0_2^+ to 0_1^+ monopole transition matrix element, and transition
radius are found in remarkable agreement with the experimental data. The
0^+_2-state structure is described as a system of three alpha-particles
oscillating between the ground-state-like configuration and the elongated chain
configuration whose probability exceeds 0.9
Valence-bond states in dynamical Jahn-Teller molecular systems
We discuss a hopping model of electrons between idealized molecular sites
with local orbital degeneracy and dynamical Jahn-Teller effect, for crystal
field environments of sufficiently high symmetry. For the Mott-insulating case
(one electron per site and large Coulomb repulsions), in the simplest two-fold
degenerate situation, we are led to consider a particular exchange hamiltonian,
describing two isotropic spin-1/2 Heisenberg problems coupled by a quartic term
on equivalent bonds. This twin-exchange hamiltonian applies to a physical
regime in which the inter-orbital singlet is the lowest-energy intermediate
state available for hopping. This regime is favored by a relatively strong
electron-phonon coupling. Using variational arguments, a large-N limit, and
exact diagonalization data, we find that the ground state, in the one
dimensional case, is a solid valence bond state. The situation in the two
dimensional case is less clear. Finally, the behavior of the system upon hole
doping is studied in one dimension.Comment: 11 pages, 5 figure
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