1,963 research outputs found
Work distribution for the driven harmonic oscillator with time-dependent strength: Exact solution and slow driving
We study the work distribution of a single particle moving in a harmonic
oscillator with time-dependent strength. This simple system has a non-Gaussian
work distribution with exponential tails. The time evolution of the
corresponding moment generating function is given by two coupled ordinary
differential equations that are solved numerically. Based on this result we
study the behavior of the work distribution in the limit of slow but finite
driving and show that it approaches a Gaussian distribution arbitrarily well
Photonic Band Gaps in 3D Network Structures with Short-range Order
We present a systematic study of photonic band gaps (PBGs) in
three-dimensional (3D) photonic amorphous structures (PAS) with short-range
order. From calculations of the density of optical states (DOS) for PAS with
different topologies, we find that tetrahedrally connected dielectric networks
produce the largest isotropic PBGs. Local uniformity and tetrahedral order are
essential to the formation of PBGs in PAS, in addition to short-range geometric
order. This work demonstrates that it is possible to create broad, isotropic
PBGs for vector light fields in 3D PAS without long-range order.Comment: 6 pages, 8 figure
Mean first-passage times of non-Markovian random walkers in confinement
The first-passage time (FPT), defined as the time a random walker takes to
reach a target point in a confining domain, is a key quantity in the theory of
stochastic processes. Its importance comes from its crucial role to quantify
the efficiency of processes as varied as diffusion-limited reactions, target
search processes or spreading of diseases. Most methods to determine the FPT
properties in confined domains have been limited to Markovian (memoryless)
processes. However, as soon as the random walker interacts with its
environment, memory effects can not be neglected. Examples of non Markovian
dynamics include single-file diffusion in narrow channels or the motion of a
tracer particle either attached to a polymeric chain or diffusing in simple or
complex fluids such as nematics \cite{turiv2013effect}, dense soft colloids or
viscoelastic solution. Here, we introduce an analytical approach to calculate,
in the limit of a large confining volume, the mean FPT of a Gaussian
non-Markovian random walker to a target point. The non-Markovian features of
the dynamics are encompassed by determining the statistical properties of the
trajectory of the random walker in the future of the first-passage event, which
are shown to govern the FPT kinetics.This analysis is applicable to a broad
range of stochastic processes, possibly correlated at long-times. Our
theoretical predictions are confirmed by numerical simulations for several
examples of non-Markovian processes including the emblematic case of the
Fractional Brownian Motion in one or higher dimensions. These results show, on
the basis of Gaussian processes, the importance of memory effects in
first-passage statistics of non-Markovian random walkers in confinement.Comment: Submitted version. Supplementary Information can be found on the
Nature website :
http://www.nature.com/nature/journal/v534/n7607/full/nature18272.htm
Oxygen isotope effect and phase separation in the optical conductivity of (LaPr)CaMnO thin films
The optical conductivities of films of
(LaPr)CaMnO with different oxygen isotopes
(O and O) have been determined in the spectral range from 0.3 to
4.3 eV using a combination of transmission in the mid-infrared and ellipsometry
from the near-infrared to ultra-violet regions. We have found that the isotope
exchange strongly affects the optical response in the ferromagnetic phase in a
broad frequency range, in contrast to the almost isotope-independent optical
conductivity above . The substitution by O strongly suppresses the
Drude response and a mid-infrared peak while enhancing the conductivity peak at
1.5 eV. A qualitative explanation can be given in terms of the phase separation
present in these materials. Moreover, the optical response is similar to the
one extracted from measurements in polished samples and other thin films, which
signals to the importance of internal strain.Comment: 11 pages, 11 figures, to appear in PR
Josephson Plasma in RuSr2GdCu2O8
Josephson plasma in RuSrGdCuO,
RuSrGdCuO (x = 0.3), and
RuSrEuCeCuO (x = 0.5) compounds is
investigated by the sphere resonance method. The Josephson plasma is observed
in a low-frequency region (around 8.5 cm at T ) for
ferromagnetic RuSrGdCuO, while it increases to 35 cm
for non-ferromagnetic RuSrGdCuO (x = 0.3), which
represents a large reduction in the Josephson coupling at ferromagnetic
RuO block layers. The temperature dependence of the plasma does not shift
to zero frequency ({\it i.e.} = 0) at low temperatures, indicating that
there is no transition from the 0-phase to the -phase in these compounds.
The temperature dependence and the oscillator strength of the peak are
different from those of other non-magnetic cuprates, and the origins of these
anomalies are discussed.Comment: to appear in Phys. Rev.B Rapid Com
Measuring the elements of the optical density matrix
Most methods for experimentally reconstructing the quantum state of light
involve determining a quasiprobability distribution such as the Wigner
function. In this paper we present a scheme for measuring individual density
matrix elements in the photon number state representation. Remarkably, the
scheme is simple, involving two beam splitters and a reference field in a
coherent state.Comment: 6 pages and 1 figur
Evidence of metallic clustering in annealed Ga1-xMnxAs from atypical scaling behavior of the anomalous Hall coefficient
We report on the anomalous Hall coefficient and longitudinal resistivity
scaling relationships on a series of annealed Ga1-xMnxAs epilayers (x~0.055).
As-grown samples exhibit scaling parameter n of ~ 1. Near the optimal annealing
temperature, we find n ~ 2 to be consistent with recent theories on the
intrinsic origins of anomalous Hall Effect in Ga1-xMnxAs. For annealing
temperatures far above the optimum, we note n > 3, similar behavior to certain
inhomogeneous systems. This observation of atypical behavior agrees well with
characteristic features attributable to spherical resonance from metallic
inclusions from optical spectroscopy measurements.Comment: 3 pages, 3 figure
Single domain transport measurements of C60 films
Thin films of potassium doped C60, an organic semiconductor, have been grown
on silicon. The films were grown in ultra-high vacuum by thermal evaporation of
C60 onto oxide-terminated silicon as well as reconstructed Si(111). The
substrate termination had a drastic influence on the C60 growth mode which is
directly reflected in the electrical properties of the films. Measured on the
single domain length scale, these films revealed resistivities comparable to
bulk single crystals. In situ electrical transport properties were correlated
to the morphology of the film determined by scanning tunneling microscopy. The
observed excess conductivity above the superconducting transition can be
attributed to two-dimensional fluctuations.Comment: 4 pages, 4 figure
Disorder Driven Critical Behavior of Periodic Elastic Media in a Crystal Potential
We study a lattice model of a three-dimensional periodic elastic medium at
zero temperature with exact combinatorial optimization methods. A competition
between pinning of the elastic medium, representing magnetic flux lines in the
mixed phase of a superconductor or charge density waves in a crystal, by
randomly distributed impurities and a periodic lattice potential gives rise to
a continuous phase transition from a flat phase to a rough phase. We determine
the critical exponents of this roughening transition via finite size scaling
obtaining , , and find
that they are universal with respect to the periodicity of the lattice
potential. The small order parameter exponent is reminiscent of the random
field Ising critical behavior in 3.Comment: 4 pages, 3 eps-figures include
Highly Resistive and Ultrafast FeâIon Implanted InGaAs for the Applications of THz Photomixer and Photoconductive Switch
We develop highlyâresistive (i.e. lowâcarrierâdensity) and ultrafast Feâion implanted InGaAs layers for the applications of THz photomixer and photoconductive switch. The measured Hall mobility, sheet resistance, carrier density, and carrier lifetime of the optimized 1.2âÎŒmâthick Feâimplanted InGaAs layer are 3.4Ă102 cm2/Vs, 0.24 MΩ, 6.5Ă1014 cmâ3, and 0.13ps, respectively
- âŠ