1,693 research outputs found
Fluctuation effects in disordered Peierls systems
We review the density of states and related quantities of quasi
one-dimensional disordered Peierls systems in which fluctuation effects of a
backscattering potential play a crucial role. The low-energy behavior of
non-interacting fermions which are subject to a static random backscattering
potential will be described by the fluctuating gap model (FGM). Recently, the
FGM has also been used to explain the pseudogap phenomenon in high-
superconductors. After an elementary introduction to the FGM in the context of
commensurate and incommensurate Peierls chains, we develop a non-perturbative
method which allows for a simultaneous calculation of the density of states
(DOS) and the inverse localization length. First, we recover all known results
in the limits of zero and infinite correlation lengths of the random potential.
Then, we attack the problem of finite correlation lengths. While a complex
order parameter, which describes incommensurate Peierls chains, leads to a
suppression of the DOS, i.e. a pseudogap, the DOS exhibits a singularity at the
Fermi energy if the order parameter is real and therefore refers to a
commensurate system. We confirm these results by calculating the DOS and the
inverse localization length for finite correlation lengths and Gaussian
statistics of the backscattering potential with unprecedented accuracy
numerically. Finally, we consider the case of classical phase fluctuations
which apply to low temperatures where amplitude fluctuations are frozen out. In
this physically important regime, which is also characterized by finite
correlation lengths, we present analytic results for the DOS, the inverse
localization length, the specific heat, and the Pauli susceptibility.Comment: 60 pages, 16 figure
Ultra-Short Optical Pulse Generation with Single-Layer Graphene
Pulses as short as 260 fs have been generated in a diode-pumped low-gain
Er:Yb:glass laser by exploiting the nonlinear optical response of single-layer
graphene. The application of this novel material to solid-state bulk lasers
opens up a way to compact and robust lasers with ultrahigh repetition rates.Comment: 6 pages, 3 figures, to appear in Journal of Nonlinear Optical Physics
& Material
Finite-temperature scalar fields and the cosmological constant in an Einstein universe
We study the back reaction effect of massless minimally coupled scalar field
at finite temperatures in the background of Einstein universe. Substituting for
the vacuum expectation value of the components of the energy-momentum tensor on
the RHS of the Einstein equation, we deduce a relationship between the radius
of the universe and its temperature. This relationship exhibit a maximum
temperature, below the Planck scale, at which the system changes its behaviour
drastically. The results are compared with the case of a conformally coupled
field. An investigation into the values of the cosmological constant exhibit a
remarkable difference between the conformally coupled case and the minimally
coupled one.Comment: 7 pages, 2 figure
Phenomenon of the time-reversal-violating photon polarization plane rotation by a gas placed to an electric field
T-odd P-odd phenomenon of the photon polarization plane rotation (circular
dichroism) is considered for an atomic (molecules) gas placed to an electric
field. The expression for the T non-invariant polarizability of an atom
(molecule) placed to an electric field is obtained. It is shown that the T-odd
plane rotation angle increases when the interaction energy of an atom
(molecule) with an electric field is the same order as the opposite parity
levels spacing.Comment: 9 pages, Late
Electron-electron interaction and charging effects in graphene quantum dots
We analyze charging effects in graphene quantum dots. Using a simple model,
we show that, when the Fermi level is far from the neutrality point, charging
effects lead to a shift in the electrostatic potential and the dot shows
standard Coulomb blockade features. Near the neutrality point, surface states
are partially occupied and the Coulomb interaction leads to a strongly
correlated ground state which can be approximated by either a Wigner crystal or
a Laughlin like wave function. The existence of strong correlations modify the
transport properties which show non equilibrium effects, similar to those
predicted for tunneling into other strongly correlated systems.Comment: Extended version accepted for publication at Phys. Rev.
Hadamard States and Adiabatic Vacua
Reversing a slight detrimental effect of the mailer related to TeXabilityComment: 10pages, LaTeX (RevTeX-preprint style
Initial basalt target site selection evaluation for the Mars penetrator drop test
Potential basalt target sites for an air drop penetrator test were described and the criteria involved in site selection were discussed. A summary of the background field geology and recommendations for optimum sites are also presented
The Introduction of a Multimodal Clinical Pathway for Outpatient Total Knee Arthroplasty in the Era of COVID-19
The combination of a short acting spinal and muscle-sparing regional blocks, including adductor canal and iPACK blocks, can allow for successful outpatient total knee arthroplasty.https://knowledgeconnection.mainehealth.org/lambrew-retreat-2021/1050/thumbnail.jp
Energy Density in Expanding Universes as Seen by Unruh's Detector
We consider the response of an Unruh detector to scalar fields in an
expanding space-time. When combining transition elements of the scalar field
Hamiltonian with the interaction operator of detector and field, one finds at
second order in time-dependent perturbation theory a transition amplitude,
which actually dominates in the ultraviolet over the first order contribution.
In particular, the detector response faithfully reproduces the particle number
implied by the stress-energy of a minimally coupled scalar field, which is
inversely proportional to the energy of a scalar mode. This finding disagrees
with the contention that in de Sitter space, the response of the detector drops
exponentially with particle energy and therefore indicates a thermal spectrum.Comment: 15 pages, 1 figur
Electronic states and Landau levels in graphene stacks
We analyze, within a minimal model that allows analytical calculations, the
electronic structure and Landau levels of graphene multi-layers with different
stacking orders. We find, among other results, that electrostatic effects can
induce a strongly divergent density of states in bi- and tri-layers,
reminiscent of one-dimensional systems. The density of states at the surface of
semi-infinite stacks, on the other hand, may vanish at low energies, or show a
band of surface states, depending on the stacking order
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