15,555 research outputs found
Band and momentum dependent electron dynamics in superconducting as seen via electronic Raman scattering
We present details of carrier properties in high quality single crystals obtained from electronic Raman
scattering. The experiments indicate a strong band and momentum anisotropy of
the electron dynamics above and below the superconducting transition
highlighting the importance of complex band-dependent interactions. The
presence of low energy spectral weight deep in the superconducting state
suggests a gap with accidental nodes which may be lifted by doping and/or
impurity scattering. When combined with other measurements, our observation of
band and momentum dependent carrier dynamics indicate that the iron arsenides
may have several competing superconducting ground states.Comment: 5 pages, 4 figure
Magnetism, superconductivity and coupling in cuprate heterostructures probed by low-energy muon-spin rotation
We present a low-energy muon-spin-rotation study of the magnetic and
superconducting properties of YBa2Cu3O7/PrBa2Cu3O7 trilayer and bilayer
heterostructures. By determining the magnetic-field profiles throughout these
structures we show that a finite superfluid density can be induced in otherwise
semiconducting PrBa2Cu3O7 layers when juxtaposed to YBa2Cu3O7 "electrodes"
while the intrinsic antiferromagnetic order is unaffected.Comment: 10 pages, 9 figures; figure 9 corrected in version
Evidence for the Role of Instantons in Hadron Structure from Lattice QCD
Cooling is used as a filter on a set of gluon fields sampling the Wilson
action to selectively remove essentially all fluctuations of the gluon field
except for the instantons. The close agreement between quenched lattice QCD
results with cooled and uncooled configurations for vacuum correlation
functions of hadronic currents and for density-density correlation functions in
hadronic bound states provides strong evidence for the dominant role of
instantons in determining light hadron structure and quark propagation in the
QCD vacuum.Comment: 26 pages in REVTeX, plus 10 figures, uuencoded. Submitted to Physical
Review D. MIT-CTP-226
Noncommutative electrodynamics and ultra high energy gamma rays
Plane waves in noncommutative classical electrodynamics (NCED) have a
peculiar dispersion relation. We investigate the kinematical conditions on this
deformed "mass shell" which come from ultra high energy gamma rays and discuss
noncommutative dynamical effects on the gamma absorption by the infrared
background and on the intrinsic spectrum. Finally we note that in NCED there is
a strong correlation between the modified dispersion relation and the presence
of dynamical effects in electromagnetic phenomena such as in the case of the
synchrotron radiation. From this point of view, the limits on the typical
energy scale of the violation of Lorentz invariance obtained by deformed
dispersion relations and by assuming undeformed dynamical effects should be
taken with some caution.Comment: Latex file, 7 pages, to be published in Europhysics Letter
Molecular dynamics study of the fragmentation of silicon doped fullerenes
Tight binding molecular dynamics simulations, with a non orthogonal basis
set, are performed to study the fragmentation of carbon fullerenes doped with
up to six silicon atoms. Both substitutional and adsorbed cases are considered.
The fragmentation process is simulated starting from the equilibrium
configuration in each case and imposing a high initial temperature to the
atoms. Kinetic energy quickly converts into potential energy, so that the
system oscillates for some picoseconds and eventually breaks up. The most
probable first event for substituted fullerenes is the ejection of a C2
molecule, another very frequent event being that one Si atom goes to an
adsorbed position. Adsorbed Si clusters tend to desorb as a whole when they
have four or more atoms, while the smaller ones tend to dissociate and
sometimes interchange positions with the C atoms. These results are compared
with experimental information from mass abundance spectroscopy and the products
of photofragmentation.Comment: Seven two-column pages, six postscript figures. To be published in
Physical Review
Non-Relativistic Gravitation: From Newton to Einstein and Back
We present an improvement to the Classical Effective Theory approach to the
non-relativistic or Post-Newtonian approximation of General Relativity. The
"potential metric field" is decomposed through a temporal Kaluza-Klein ansatz
into three NRG-fields: a scalar identified with the Newtonian potential, a
3-vector corresponding to the gravito-magnetic vector potential and a 3-tensor.
The derivation of the Einstein-Infeld-Hoffmann Lagrangian simplifies such that
each term corresponds to a single Feynman diagram providing a clear physical
interpretation. Spin interactions are dominated by the exchange of the
gravito-magnetic field. Leading correction diagrams corresponding to the 3PN
correction to the spin-spin interaction and the 2.5PN correction to the
spin-orbit interaction are presented.Comment: 10 pages, 3 figures. v2: published version. v3: Added a computation
of Einstein-Infeld-Hoffmann in higher dimensions within our improved ClEFT
which partially confirms and partially corrects a previous computation. See
notes added at end of introductio
Resonant Enhancement of Charge Density Wave Diffraction in the Rare-Earth Tritellurides
We performed resonant soft X-ray diffraction on known charge density wave
(CDW) compounds, rare earth tri-tellurides. Near the (3d - 4f) absorption
edge of rare earth ions, an intense diffraction peak is detected at a
wavevector identical to that of CDW state hosted on Te planes, indicating a
CDW-induced modulation on the rare earth ions. Surprisingly, the temperature
dependence of the diffraction peak intensity demonstrates an exponential
increase at low temperatures, vastly different than that of the CDW order
parameter. Assuming 4f multiplet splitting due to the CDW states,we present a
model to calculate X-ray absorption spectrum and resonant profile of the
diffraction peak, agreeing well with experimental observations. Our results
demonstrate a situation where the temperature dependence of resonant X-ray
diffraction peak intensity is not directly related to the intrinsic behavior of
the order parameter associated with the electronic order, but is dominated by
the thermal occupancy of the valence states.Comment: 7 pages, 5 figure
Scaling properties of cavity-enhanced atom cooling
We extend an earlier semiclassical model to describe the dissipative motion
of N atoms coupled to M modes inside a coherently driven high-finesse cavity.
The description includes momentum diffusion via spontaneous emission and cavity
decay. Simple analytical formulas for the steady-state temperature and the
cooling time for a single atom are derived and show surprisingly good agreement
with direct stochastic simulations of the semiclassical equations for N atoms
with properly scaled parameters. A thorough comparison with standard free-space
Doppler cooling is performed and yields a lower temperature and a cooling time
enhancement by a factor of M times the square of the ratio of the atom-field
coupling constant to the cavity decay rate. Finally it is shown that laser
cooling with negligible spontaneous emission should indeed be possible,
especially for relatively light particles in a strongly coupled field
configuration.Comment: 7 pages, 5 figure
Thermal expansion, heat capacity and magnetostriction of RAl (R = Tm, Yb, Lu) single crystals
We present thermal expansion and longitudinal magnetostriction data for cubic
RAl3 (R = Tm, Yb, Lu) single crystals. The thermal expansion coefficient for
YbAl3 is consistent with an intermediate valence of the Yb ion, whereas the
data for TmAl3 show crystal electric field contributions and have strong
magnetic field dependencies. de Haas-van Alphen-like oscillations were observed
in the magnetostriction data of YbAl3 and LuAl3, several new extreme orbits
were measured and their effective masses were estimated. Zero and 140 kOe
specific heat data taken on both LuAl3 and TmAl3 for T < 200 K allow for the
determination of a CEF splitting scheme for TmAl3
Dynamical generation of fuzzy extra dimensions, dimensional reduction and symmetry breaking
We present a renormalizable 4-dimensional SU(N) gauge theory with a suitable
multiplet of scalar fields, which dynamically develops extra dimensions in the
form of a fuzzy sphere S^2. We explicitly find the tower of massive
Kaluza-Klein modes consistent with an interpretation as gauge theory on M^4 x
S^2, the scalars being interpreted as gauge fields on S^2. The gauge group is
broken dynamically, and the low-energy content of the model is determined.
Depending on the parameters of the model the low-energy gauge group can be
SU(n), or broken further to SU(n_1) x SU(n_2) x U(1), with mass scale
determined by the size of the extra dimension.Comment: 27 pages. V2: discussion and references added, published versio
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