691 research outputs found
Rapidly driven nanoparticles: Mean first-passage times and relaxation of the magnetic moment
We present an analytical method of calculating the mean first-passage times
(MFPTs) for the magnetic moment of a uniaxial nanoparticle which is driven by a
rapidly rotating, circularly polarized magnetic field and interacts with a heat
bath. The method is based on the solution of the equation for the MFPT derived
from the two-dimensional backward Fokker-Planck equation in the rotating frame.
We solve these equations in the high-frequency limit and perform precise,
numerical simulations which verify the analytical findings. The results are
used for the description of the rates of escape from the metastable domains
which in turn determine the magnetic relaxation dynamics. A main finding is
that the presence of a rotating field can cause a drastic decrease of the
relaxation time and a strong magnetization of the nanoparticle system. The
resulting stationary magnetization along the direction of the easy axis is
compared with the mean magnetization following from the stationary solution of
the Fokker-Planck equation.Comment: 24 pages, 4 figure
Bandwidth tuning triggers interplay of charge order and superconductivity in two-dimensional organic materials
We observe charge-order fluctuations in the quasi-two-dimensional organic
superconductor -(BEDT-TTF)2 SF5 CH2 CF2 SO3 both by means
of vibrational spectroscopy, locally probing the fluctuating charge order, and
investigating the in-plane dynamical response by infrared reflectance
spectroscopy. The decrease of effective electronic interaction in an
isostructural metal suppresses both charge-order fluctuations and
superconductivity, pointing on their interplay. We compare the results of our
experiments with calculations on the extended Hubbard model.Comment: 5 pages, 4 figure
Decision and function problems based on boson sampling
Boson sampling is a mathematical problem that is strongly believed to be
intractable for classical computers, whereas passive linear interferometers can
produce samples efficiently. So far, the problem remains a computational
curiosity, and the possible usefulness of boson-sampling devices is mainly
limited to the proof of quantum supremacy. The purpose of this work is to
investigate whether boson sampling can be used as a resource of decision and
function problems that are computationally hard, and may thus have
cryptographic applications. After the definition of a rather general
theoretical framework for the design of such problems, we discuss their
solution by means of a brute-force numerical approach, as well as by means of
non-boson samplers. Moreover, we estimate the sample sizes required for their
solution by passive linear interferometers, and it is shown that they are
independent of the size of the Hilbert space.Comment: Close to the version published in PR
Thermal activation between Landau levels in the organic superconductor -(BEDT-TTF)SFCHCFSO
We show that Shubnikov-de Haas oscillations in the interlayer resistivity of
the organic superconductor -(BEDT-TTF)SF
CHCFSO become very pronounced in magnetic fields ~60~T.
The conductivity minima exhibit thermally-activated behaviour that can be
explained simply by the presence of a Landau gap, with the
quasi-one-dimensional Fermi surface sheets contributing negligibly to the
conductivity. This observation, together with complete suppression of chemical
potential oscillations, is consistent with an incommensurate nesting
instability of the quasi-one-dimensional sheets.Comment: 6 pages, 4 figure
On the de Haas - van Alphen oscillations in quasi-two-dimensional metals: effect of the Fermi surface curvature
Here, we present the results of theoretical analysis of the de Haas-van
Alphen oscillations in quasi-two-dimensional normal metals. We had been
studying effects of the Fermi surface (FS) shape on these oscillations. It was
shown that the effects could be revealed and well pronounced when the FS
curvature becomes zero at cross-sections with extremal cross-sectional areas.
In this case both shape and amplitude of the oscillations could be
significantly changed. Also, we analyze the effect of the FS local geometry on
the angular dependencies of the oscillation amplitudes when the magnetic field
is tilted away from the FS symmetry axis by the angle We show that a
peak appears at whose height could be of the same order as
the maximum at the Yamaji angle. This peak emerges when the FS includes zero
curvature cross-sections of extremal areas. Such maximum was observed in
experiments on the The obtained results could be
applied to organic metals and other quasi-two-dimensional compounds.Comment: 9 pages, 4 figures, text added, references adde
Fucking failures: The future of fat sex
In the context of the obesity âepidemicâ fat peopleâs sex lives are cast as sterile, sexually dysfunctional or just plain non-existent. This article analyzes medical discourses of obesity and sex in order to argue that fat sex is constructed as a type of failure. Using insights from antisocial queer theory, fat sex is further shown to be queer in its failure to adhere to the specifically heteronormative dictates of what Edelman (2004) calls âreproductive futurismâ. The analysis finally engages with Halberstamâs (2011) notion of queer failure to demonstrate how deconstructing notions of success and failure might offer fat political projects new ways to imagine the future of fat sex
Coherent vs incoherent interlayer transport in layered metals
The magnetic-field, temperature, and angular dependence of the interlayer
magnetoresistance of two different quasi-two-dimensional (2D) organic
superconductors is reported. For -(BEDT-TTF)I we find a
well-resolved peak in the angle-dependent magnetoresistance at (field parallel to the layers). This clear-cut proof for the coherent
nature of the interlayer transport is absent for
''-(BEDT-TTF)SFCHCFSO. This and the non-metallic
behavior of the magnetoresistance suggest an incoherent quasiparticle motion
for the latter 2D metal.Comment: 4 pages, 4 figures. Phys. Rev. B, in pres
L-Edge Spectroscopy of Dilute, Radiation-Sensitive Systems Using a Transition-Edge-Sensor Array
We present X-ray absorption spectroscopy and resonant inelastic X-ray
scattering (RIXS) measurements on the iron L-edge of 0.5 mM aqueous
ferricyanide. These measurements demonstrate the ability of high-throughput
transition-edge-sensor (TES) spectrometers to access the rich soft X-ray
(100-2000eV) spectroscopy regime for dilute and radiation-sensitive samples.
Our low-concentration data are in agreement with high-concentration
measurements recorded by conventional grating-based spectrometers. These
results show that soft X-ray RIXS spectroscopy acquired by high-throughput TES
spectrometers can be used to study the local electronic structure of dilute
metal-centered complexes relevant to biology, chemistry and catalysis. In
particular, TES spectrometers have a unique ability to characterize frozen
solutions of radiation- and temperature-sensitive samples.Comment: 19 pages, 4 figure
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