9,489 research outputs found
Fidelity susceptibility in the two-dimensional spin-orbit models
We study the quantum phase transitions in the two-dimensional spin-orbit
models in terms of fidelity susceptibility and reduced fidelity susceptibility.
An order-to-order phase transition is identified by fidelity susceptibility in
the two-dimensional Heisenberg XXZ model with Dzyaloshinsky-Moriya interaction
on a square lattice. The finite size scaling of fidelity susceptibility shows a
power-law divergence at criticality, which indicates the quantum phase
transition is of second order. Two distinct types of quantum phase transitions
are witnessed by fidelity susceptibility in Kitaev-Heisenberg model on a
hexagonal lattice. We exploit the symmetry of two-dimensional quantum compass
model, and obtain a simple analytic expression of reduced fidelity
susceptibility. Compared with the derivative of ground-state energy, the
fidelity susceptibility is a bit more sensitive to phase transition. The
violation of power-law behavior for the scaling of reduced fidelity
susceptibility at criticality suggests that the quantum phase transition
belongs to a first-order transition. We conclude that fidelity susceptibility
and reduced fidelity susceptibility show great advantage to characterize
diverse quantum phase transitions in spin-orbit models.Comment: 11 pages. 11 figure
Suppression of the superconducting energy gap in intrinsic Josephson junctions of single crystals
We have observed back-bending structures at high bias current in the
current-voltage curves of intrinsic Josephson junctions. These structures may
be caused by nonequilibrium quasiparticle injection and/or Joule heating. The
energy gap suppression varies considerably with temperature. Different levels
of the suppression are observed when the same level of current passes through
top electrodes of different sizes. Another effect which is seen and discussed,
is a super-current ``reentrance'' of a single intrinsic Josephson junction with
high bias current.Comment: accepted by Supercond. Sci. and Tech., 200
A discrete time-dependent method for metastable atoms in intense fields
The full-dimensional time-dependent Schrodinger equation for the electronic
dynamics of single-electron systems in intense external fields is solved
directly using a discrete method.
Our approach combines the finite-difference and Lagrange mesh methods. The
method is applied to calculate the quasienergies and ionization probabilities
of atomic and molecular systems in intense static and dynamic electric fields.
The gauge invariance and accuracy of the method is established. Applications to
multiphoton ionization of positronium and hydrogen atoms and molecules are
presented. At very high intensity above saturation threshold, we extend the
method using a scaling technique to estimate the quasienergies of metastable
states of the hydrogen molecular ion. The results are in good agreement with
recent experiments.Comment: 10 pages, 9 figure, 4 table
Radiative and Collisional Jet Energy Loss in the Quark-Gluon Plasma at RHIC
We calculate and compare bremsstrahlung and collisional energy loss of hard
partons traversing a quark-gluon plasma. Our treatment of both processes is
complete at leading order in the coupling and accounts for the probabilistic
nature of the jet energy loss. We find that the nuclear modification factor
for neutral production in heavy ion collisions is sensitive to
the inclusion of collisional and radiative energy loss contributions while the
averaged energy loss only slightly increases if collisional energy loss is
included for parent parton energies . These results are important for
the understanding of jet quenching in Au+Au collisions at at
RHIC. Comparison with data is performed applying the energy loss calculation to
a relativistic ideal (3+1)-dimensional hydrodynamic description of the
thermalized medium formed at RHIC.Comment: 4 pages, 3 figure
Dissociation spectrum of H from a short, intense infrared laser pulse: vibration structure and focal volume effects
The dissociation spectrum of the hydrogen molecular ion by short intense
pulses of infrared light is calculated. The time-dependent Schr\"odinger
equation is discretized and integrated in position and momentum space. For
few-cycle pulses one can resolve vibrational structure that commonly arises in
the experimental preparation of the molecular ion from the neutral molecule. We
calculate the corresponding energy spectrum and analyze the dependence on the
pulse time-delay, pulse length, and intensity of the laser for nm. We conclude that the proton spectrum is a both a sensitive probe of the
vibrational dynamics and the laser pulse. Finally we compare our results with
recent measurements of the proton spectrum for 55 fs pulses using a Ti:Sapphire
laser (nm). Integrating over the laser focal volume, for the
intensity W cm, we find our results are in
excellent agreement with these experiments.Comment: 17 pages, 8 figures, preprin
Complete Nondiagonal Reflection Matrices of RSOS/SOS and Hard Hexagon Models
In this paper we compute the most general nondiagonal reflection matrices of
the RSOS/SOS models and hard hexagon model using the boundary Yang-Baxter
equations. We find new one-parameter family of reflection matrices for the RSOS
model in addition to the previous result without any parameter. We also find
three classes of reflection matrices for the SOS model, which has one or two
parameters. For the hard hexagon model which can be mapped to RSOS(5) model by
folding four RSOS heights into two, the solutions can be obtained similarly
with a main difference in the boundary unitarity conditions. Due to this, the
reflection matrices can have two free parameters. We show that these extra
terms can be identified with the `decorated' solutions. We also generalize the
hard hexagon model by `folding' the RSOS heights of the general RSOS(p) model
and show that they satisfy the integrability conditions such as the Yang-
Baxter and boundary Yang-Baxter equations. These models can be solved using the
results for the RSOS models.Comment: 18pages,Late
Magnetic properties of an SU(4) spin-orbital chain
In this paper, we study the magnetic properties of the one-dimensional SU(4)
spin-orbital model by solving its Bethe ansatz solution numerically. It is
found that the magnetic properties of the system for the case of
differs from that for the case of . The magnetization curve and
susceptibility are obtained for a system of 200 sites. For , the
phase diagram depending on the magnetic field and the ratio of Land\'e factors,
, is obtained. Four phases with distinct magnetic properties are
found.Comment: 4 pages, 2 figure
Matrix Product State and Quantum Phase Transitions in the One-Dimensional Extended Quantum Compass Model
The matrix product state (MPS) is utilized to study the ground state
properties and quantum phase transitions (QPTs) of the one-dimensional quantum
compass model (QCM). The MPS wavefunctions are argued to be very efficient
descriptions of QCM ground states, and are numerically determined by imaginary
time projections. The ground state energy, correlations, quantum entanglement
and its spectrum, local and nonlocal order parameters, etc., are calculated and
studied in details. It is revealed that the bipartite and block entanglement
entropies, as well as the nearest neighbor correlation functions can be used to
detect the second-order QPTs, but not the first-order ones, while fidelity
detections can recognize both. The entanglement spectrum is extracted from the
MPS wavefunction, and found to be doubly degenerate in disordered phases of
QCM, where non-local string order parameters exist. Moreover, with linearized
tensor renormalization group method, the specific heat curves are evaluated and
their low temperature behaviors are investigated.Comment: 12 pages, 19 figure
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