23,964 research outputs found
Spin and orbital valence bond solids in a one-dimensional spin-orbital system: Schwinger boson mean field theory
A generalized one-dimensional spin-orbital model is
studied by Schwinger boson mean-field theory (SBMFT). We explore mainly the
dimer phases and clarify how to capture properly the low temperature properties
of such a system by SBMFT. The phase diagrams are exemplified. The three dimer
phases, orbital valence bond solid (OVB) state, spin valence bond solid (SVB)
state and spin-orbital valence bond solid (SOVB) state, are found to be favored
in respectively proper parameter regions, and they can be characterized by the
static spin and pseudospin susceptibilities calculated in SBMFT scheme. The
result reveals that the spin-orbit coupling of type serves
as both the spin-Peierls and orbital-Peierles mechanisms that responsible for
the spin-singlet and orbital-singlet formations respectively.Comment: 6 pages, 3 figure
Anti-shielding Effect and Negative Temperature in Instantaneously Reversed Electric Fields and Left-Handed Media
The connections between the anti-shielding effect, negative absolute
temperature and superluminal light propagation in both the instantaneously
reversed electric field and the left-handed media are considered in the present
paper. The instantaneous inversion of the exterior electric field may cause the
electric dipoles into the state of negative absolute temperature and therefore
give rise to a negative effective mass term of electromagnetic field (i. e.,
the electromagnetic field propagating inside the negative-temperature medium
will acquire an imaginary rest mass), which is said to result in the potential
superluminality effect of light propagation in this anti-shielding dielectric.
In left-handed media, such phenomena may also arise.Comment: 9 pages, Late
Difficulties in probing density dependent symmetry potential with the HBT interferometry
Based on the updated UrQMD transport model, the effect of the symmetry
potential energy on the two-nucleon HBT correlation is investigated with the
help of the coalescence program for constructing clusters, and the CRAB
analyzing program of the two-particle HBT correlation. An obvious non-linear
dependence of the neutron-proton (or neutron-neutron) HBT correlation function
() at small relative momenta on the stiffness factor of the
symmetry potential energy is found: when , the
increases rapidly with increasing , while it starts to saturate if
. It is also found that both the symmetry potential energy
at low densities and the conditions of constructing clusters at the late stage
of the whole process influence the two-nucleon HBT correlation with the same
power.Comment: 11 pages, 4 figure
Possible dibaryons in the quark cluster model
In the framework of RGM, the binding energy of one channel
() and are studied in the
chiral SU(3) quark cluster model. It is shown that the binding energies of the
systems are a few tens of MeV. The behavior of the chiral field is also
investigated by comparing the results with those in the SU(2) and the extended
SU(2) chiral quark models. It is found that the symmetry property of the
system makes the contribution of the relative kinetic energy
operator between two clusters attractive. This is very beneficial for forming
the bound dibaryon. Meanwhile the chiral-quark field coupling also plays a very
important role on binding. The S-wave phase shifts and the corresponding
scattering lengths of the systems are also given.Comment: LeTex with 2 ps figure
Displaced thinned coprime arrays with an additional sensor for DOA estimation
A new sparse array structure based on the recently proposed thinned coprime arrays is proposed to maximize the number of unique lags. The design process involves two stages: the first stage displaces one subarray from its original position for an increase in the number of lags; as the displacement results in the minimum interelement spacing equal to integer multiples of half-wavelength, an additional sensor at a distance of half-wavelength is then added in the displaced subarray to avoid spatial aliasing. The strategic location of the additional sensor results in a significant increase in the overall unique lags which can be utilized for direction-of-arrival estimation (DOA) using compressive sensing based methods. Furthermore, the new structure has excellent performance in the presence of mutual coupling as shown by simulation results
Unified theory of phase separation and charge ordering in doped manganite perovskites
A unified theory is developed to explain various types of electronic
collective behaviors in doped manganites RXMnO (R = La, Pr,Nd
etc. and X = Ca, Sr, Ba etc.). Starting from a realistic electronic model, we
derive an effective Hamiltonianis by ultilizing the projection perturbation
techniques and develop a spin-charge-orbital coherent state theory, in which
the Jahn-Teller effect and the orbital degeneracy of e electrons in Mn ions
are taken into account. Physically, the experimentally observed charge ordering
state and electronic phase separation are two macroscopic quantum phenomena
with opposite physical mechanisms, and their physical origins are elucidated in
this theory. Interplay of the Jahn-Teller effect, the lattice distortion as
well as the double exchange mechanism leads to different magnetic structures
and to different charge ordering patterns and phase separation.Comment: 10 ReVTEX pages with 4 figures attache
Formation of energy gap in higher dimensional spin-orbital liquids
A Schwinger boson mean field theory is developed for spin liquids in a
symmetric spin-orbital model in higher dimensions. Spin, orbital and coupled
spin-orbital operators are treated equally. We evaluate the dynamic correlation
functions and collective excitations spectra. As the collective excitations
have a finite energy gap, we conclude that the ground state is a spin-orbital
liquid with a two-fold degeneracy, which breaks the discrete spin-orbital
symmetry. Possible relevence of this spin liquid state to several realistic
systems, such as CaVV and NaSbTiO, are discussed.Comment: 4 pages with 1 figur
Self-induced charge currents in electromagnetic materials, photon effective rest mass and some related topics
The contribution of self-induced charge currents of metamaterial media to
photon effective rest mass is discussed in detail in the present paper. We
concern ourselves with two kinds of photon effective rest mass, i.e., the
frequency-dependent and frequency-independent effective rest mass. Based on
these two definitions, we calculate the photon effective rest mass in the
left-handed medium and the 2TDLM media, the latter of which is described by the
so-called two time derivative Lorentz material (2TDLM) model. Additionally, we
concentrate primarily on the torque, which is caused by the interaction between
self-induced charge currents in dilute plasma (e.g., the secondary cosmic rays)
and interstellar magnetic fields (ambient cosmic magnetic vector potentials),
acting on the torsion balance of the rotating torsion balance experiment.Comment: 11 pages, Late
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