1,119 research outputs found
Polaron self-trapping in a honeycomb net
Small polaron behavior in a two dimensional honeycomb net is studied by
applying the strong coupling perturbative method to the Holstein molecular
crystal model. We find that small optical polarons can be mobile also if the
electrons are strongly coupled to the lattice. Before the polarons localize and
become very heavy, there is infact a window of {\it e-ph} couplings in which
the polarons are small and have masses of order times the bare
band mass according to the value of the adiabaticity parameter. The 2D
honeycomb net favors the mobility of small optical polarons in comparison with
the square lattice.Comment: 6 pages, 3 figures, to appear in J.Phys.:Condensed Matter {PACS:
63.10.+a, 63.20.Dj, 71.38.+i
Electron locking in semiconductor superlattices
We describe a novel state of electrons and phonons arising in semiconductor
superlattices (SSL) due to strong electron-phonon interactions. These states
are characterized by a localization of phonons and a self-trapping or locking
of electrons in one or several quantum wells due to an additional,
deformational potential arising around these locking wells in SSL. The effect
is enhanced in a longitudinal magnetic field.
Using the tight-binding and adiabatic approximations the whole energy
spectrum of the self-trapped states is found and accurate, analytic expressions
are included for strong electron-phonon coupling. Finally, we discuss possible
experiments which may detect these predicted self-trapped states.Comment: 8 pages, 2 figures. Please note that the published article has the
title 'Electron locking in layered structures by a longitudinal magnetic
field
Pion and Kaon Polarizabilities and Radiative Transitions
CERN COMPASS plans measurements of gamma-pi and gamma-K interactions using
50-280 GeV pion (kaon) beams and a virtual photon target. Pion (kaon)
polarizabilities and radiative transitions will be measured via Primakoff
effect reactions such as pi+gamma->pi'+gamma and pi+gamma->meson. The former
can test a precise prediction of chiral symmetry; the latter for
pi+gamma->a1(1260) is important for understanding the polarizability. The
radiative transition of a pion to a low mass two-pion system, pi+gamma->pi+pi0,
can also be studied to measure the chiral anomaly amplitude F(3pi)
(characterizing gamma->3pi), arising from the effective Chiral Lagrangian. We
review here the motivation for the above physics program. We describe the beam,
target, detector, and trigger requirements for these experiments. We also
describe FNAL SELEX attempts to study related physics via the interaction of
600 GeV pions with target electrons. Data analysis in progress aims to identify
the reactions pi+e->pi'+e'+pi0 related to the chiral anomaly, and
pi+e->pi'+e'+gamma related to pion polarizabilities.Comment: 16 pages, 6 figures, Latex Springer-Verlag style Tel Aviv U. Preprint
TAUP-2469-97, Contribution to the Workshop on Chiral Dynamics Theory and
Experiment, U. of Mainz, Sept. 1-5, 1997, to be published in Springer-Verlag,
Eds. A. Bernstein, Th. Walcher, 199
Long Range Electromagnetic Effects involving Neutral Systems and Effective Field Theory
We analyze the electromagnetic scattering of massive particles with and
without spin wherein one particle (or both) is electrically neutral. Using the
techniques of effective field theory, we isolate the leading long distance
effects, both classical and quantum mechanical. For spinless systems results
are identical to those obtained earlier via more elaborate dispersive methods.
However, we also find new results if either or both particles carry apin.Comment: 23 pages, 3 .eps figure
On Quantum Groups in the Hubbard Model with Phonons
The correct Hamiltonian for an extended Hubbard model with quantum group
symmetry as introduced by A. Montorsi and M. Rasetti is derived for a
D-dimensional lattice. It is shown that the superconducting SUq(2) holds as a
true quantum symmetry only for D = 1 and that terms of higher order in the
fermionic operators in addition to phonons are required for a quantum symmetric
hamiltonian. The condition for quantum symmetry is "half filling" and there is
no local electron-phonon coupling. A discussion of Quantum symmetries in
general is given in a formalism that should be readily accessible to non
Hopf-algebraists.Comment: latex, 17 page
Semileptonic Hyperon Decays and CKM Unitarity
Using a technique that is not subject to first-order SU(3) symmetry breaking
effects, we determine the element of the CKM matrix from data on
semileptonic hyperon decays. We obtain =0.2250(27). This value is of
similar precision to the one derived from , but higher and in better
agreement with the unitarity requirement, .Comment: 3 pages, 1 tabl
Mass enhancement in narrow band systems
A perturbative study of the Holstein Molecular Crystal Model which accounts
for lattice structure and dimensionality effects is presented. Antiadiabatic
conditions peculiar of narrow band materials and an intermediate to strong
electron-phonon coupling are assumed. The polaron effective mass depends
crucially in all dimensions on the intermolecular coupling strengths which also
affect the size of the lattice deformation associated with the small polaron
formation.Comment: Istituto Nazionale di Fisica della Materia - Dipartimento di
Matematica e Fisica, Istituto Nazionale di Fisica della Materia Universita'
di Camerino, 62032 Camerino, Ital
Quantum Corrections to the Reissner-Nordstrom and Kerr-Newman Metrics: Spin 1
A previous evaluation of one-photon loop corrections to the energy-momentum
tensor has been extended to particles with unit spin and speculations are
presented concerning general properties of such forms.Comment: 21 pages, 1 Figur
Giant enhancement of anisotropy by electron-phonon interaction
Anisotropic electron-phonon interaction is shown to lead to the anisotropic
polaron effect. The resulting anisotropy of the polaron band is an exponential
function of the electron-phonon coupling and might be as big as . This
also makes anisotropy very sensitive to small changes of coupling and implies
wide variations of anisotropy among compounds of similar structure. The isotope
effect on mass anisotropy is predicted. Polaron masses are obtained by an exact
Quantum Monte Carlo method. Implications for high-temperature superconductors
are briefly discussed.Comment: 5 pages, 4 figure
Non-Fermi-Liquid Specific Heat of Normal Degenerate Quark Matter
We compute the low-temperature behavior of the specific heat of normal
(non-color-superconducting) degenerate quark matter as well as that of an
ultradegenerate electron gas. Long-range magnetic interactions lead to
non-Fermi-liquid behavior with an anomalous leading term.
Depending on the thermodynamic potential used as starting point, this effect
appears as a consequence of the logarithmic singularity in the fermion
self-energy at the Fermi surface or directly as a contribution from the only
weakly screened quasistatic magnetic gauge bosons. We show that a calculation
of Boyanovsky and de Vega claiming the absence of a leading term
missed it by omitting vector boson contributions to the internal energy. Using
a formulation which collects all nonanalytic contributions in bosonic ring
diagrams, we systematically calculate corrections beyond the well-known
leading-log approximation. The higher-order terms of the low-temperature
expansion turn out to also involve fractional powers and we
explicitly determine their coefficients up to and including order as
well as the subsequent logarithmically enhanced term . We derive
also a hard-dense-loop resummed expression which contains the infinite series
of anomalous terms to leading order in the coupling and which we evaluate
numerically. At low temperatures, the resulting deviation of the specific heat
from its value in naive perturbation theory is significant in the case of
strongly coupled normal quark matter and thus of potential relevance for the
cooling rates of (proto-)neutron stars with a quark matter component.Comment: REVTEX, 26 pages, 5 postscript figures. v3: new chapter added which
performs a complete hard-dense-loop resummation, covering the infinite series
of anomalous terms and extending the range of applicability to all T << m
- …