8,321 research outputs found
Photoemission evidence for crossover from Peierls-like to Mott-like transition in highly strained VO
We present a spectroscopic study that reveals that the metal-insulator
transition of strained VO thin films may be driven towards a purely
electronic transition, which does not rely on the Peierls dimerization, by the
application of mechanical strain. Comparison with a moderately strained system,
which does involve the lattice, demonstrates the crossover from Peierls- to
Mott-like transitions
Newborn screening for biotinidase deficiency in Brazil: biochemical and molecular characterizations
Parallelisable Heterotic Backgrounds
We classify the simply-connected supersymmetric parallelisable backgrounds of
heterotic supergravity. They are all given by parallelised Lie groups admitting
a bi-invariant lorentzian metric. We find examples preserving 4, 8, 10, 12, 14
and 16 of the 16 supersymmetries.Comment: 17 pages, AMSLaTe
Biomolecular imaging and electronic damage using X-ray free-electron lasers
Proposals to determine biomolecular structures from diffraction experiments
using femtosecond X-ray free-electron laser (XFEL) pulses involve a conflict
between the incident brightness required to achieve diffraction-limited atomic
resolution and the electronic and structural damage induced by the
illumination. Here we show that previous estimates of the conditions under
which biomolecular structures may be obtained in this manner are unduly
restrictive, because they are based on a coherent diffraction model that is not
appropriate to the proposed interaction conditions. A more detailed imaging
model derived from optical coherence theory and quantum electrodynamics is
shown to be far more tolerant of electronic damage. The nuclear density is
employed as the principal descriptor of molecular structure. The foundations of
the approach may also be used to characterize electrodynamical processes by
performing scattering experiments on complex molecules of known structure.Comment: 16 pages, 2 figure
Thermodynamic Properties of the One-Dimensional Extended Quantum Compass Model in the Presence of a Transverse Field
The presence of a quantum critical point can significantly affect the
thermodynamic properties of a material at finite temperatures. This is
reflected, e.g., in the entropy landscape S(T; c) in the vicinity of a quantum
critical point, yielding particularly strong variations for varying the tuning
parameter c such as magnetic field. In this work we have studied the
thermodynamic properties of the quantum compass model in the presence of a
transverse field. The specific heat, entropy and cooling rate under an
adiabatic demagnetization process have been calculated. During an adiabatic
(de)magnetization process temperature drops in the vicinity of a field-induced
zero-temperature quantum phase transitions. However close to field-induced
quantum phase transitions we observe a large magnetocaloric effect
Representations of the Canonical group, (the semi-direct product of the Unitary and Weyl-Heisenberg groups), acting as a dynamical group on noncommuting extended phase space
The unitary irreducible representations of the covering group of the Poincare
group P define the framework for much of particle physics on the physical
Minkowski space P/L, where L is the Lorentz group. While extraordinarily
successful, it does not provide a large enough group of symmetries to encompass
observed particles with a SU(3) classification. Born proposed the reciprocity
principle that states physics must be invariant under the reciprocity transform
that is heuristically {t,e,q,p}->{t,e,p,-q} where {t,e,q,p} are the time,
energy, position, and momentum degrees of freedom. This implies that there is
reciprocally conjugate relativity principle such that the rates of change of
momentum must be bounded by b, where b is a universal constant. The appropriate
group of dynamical symmetries that embodies this is the Canonical group C(1,3)
= U(1,3) *s H(1,3) and in this theory the non-commuting space Q= C(1,3)/
SU(1,3) is the physical quantum space endowed with a metric that is the second
Casimir invariant of the Canonical group, T^2 + E^2 - Q^2/c^2-P^2/b^2 +(2h
I/bc)(Y/bc -2) where {T,E,Q,P,I,Y} are the generators of the algebra of
Os(1,3). The idea is to study the representations of the Canonical dynamical
group using Mackey's theory to determine whether the representations can
encompass the spectrum of particle states. The unitary irreducible
representations of the Canonical group contain a direct product term that is a
representation of U(1,3) that Kalman has studied as a dynamical group for
hadrons. The U(1,3) representations contain discrete series that may be
decomposed into infinite ladders where the rungs are representations of U(3)
(finite dimensional) or C(2) (with degenerate U(1)* SU(2) finite dimensional
representations) corresponding to the rest or null frames.Comment: 25 pages; V2.3, PDF (Mathematica 4.1 source removed due to technical
problems); Submitted to J.Phys.
Enhancement of the electronic contribution to the low temperature specific heat of Fe/Cr magnetic multilayer
We measured the low temperature specific heat of a sputtered
magnetic multilayer, as well as separate
thick Fe and Cr films. Magnetoresistance and magnetization
measurements on the multilayer demonstrated antiparallel coupling between the
Fe layers. Using microcalorimeters made in our group, we measured the specific
heat for and in magnetic fields up to for the multilayer. The
low temperature electronic specific heat coefficient of the multilayer in the
temperature range is . This is
significantly larger than that measured for the Fe or Cr films (5.4 and respectively). No magnetic field dependence of was
observed up to . These results can be explained by a softening of the
phonon modes observed in the same data and the presence of an Fe-Cr alloy phase
at the interfaces.Comment: 20 pages, 5 figure
Nucleotide Sequence of an Operon in Nostoc sp. Strain ATCC 29133 Encoding Four Genes of the Oxidative Pentose Phosphate Cycle
Superconducting 2D system with lifted spin degeneracy: Mixed singlet-triplet state
Motivated by recent experimental findings, we have developed a theory of the
superconducting state for 2D metals without inversion symmetry modeling the
geometry of a surface superconducting layer in a field-effect-transistor or
near the boundary doped by adsorbed ions. In such systems the two-fold spin
degeneracy is lifted by spin-orbit interaction, and singlet and triplet
pairings are mixed in the wave function of the Cooper pairs. As a result, spin
magnetic susceptibility becomes anisotropic and Knight shift retains finite and
rather high value at T=0.Comment: 5 pages, no figure
Self-energy of image states on copper surfaces
We report extensive calculations of the imaginary part of the electron
self-energy in the vicinity of the (100) and (111) surfaces of Cu. The
quasiparticle self-energy is computed by going beyond a free-electron
description of the metal surface, either within the GW approximation of
many-body theory or with inclusion, within the GW approximation, of
short-range exchange-correlation effects. Calculations of the decay rate of the
first three image states on Cu(100) and the first image state on Cu(111) are
also reported, and the impact of both band structure and many-body effects on
the electron relaxation process is discussed.Comment: 8 pages, 5 figures, to appear in Phys. Rev.
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