490 research outputs found
Giant Magnetoresistance in Nanogranular Magnets
We study the giant magnetoresistance of nanogranular magnets in the presence
of an external magnetic field and finite temperature. We show that the
magnetization of arrays of nanogranular magnets has hysteretic behaviour at low
temperatures leading to a double peak in the magnetoresistance which coalesces
at high temperatures into a single peak. We numerically calculate the
magnetization of magnetic domains and the motion of domain walls in this system
using a combined mean-field approach and a model for an elastic membrane moving
in a random medium, respectively. From the obtained results, we calculate the
electric resistivity as a function of magnetic field and temperature. Our
findings show excellent agreement with various experimental data.Comment: 4 pages, 3 figure
Thermoelectric performance of weakly coupled granular materials
We study thermoelectric properties of inhomogeneous nanogranular materials
for weak tunneling conductance between the grains, g_t < 1. We calculate the
thermopower and figure of merit taking into account the shift of the chemical
potential and the asymmetry of the density of states in the vicinity of the
Fermi surface. We show that the weak coupling between the grains leads to a
high thermopower and low thermal conductivity resulting in relatively high
values of the figure of merit on the order of one. We estimate the temperature
at which the figure of merit has its maximum value for two- and
three-dimensional samples. Our results are applicable for many emerging
materials, including artificially self-assembled nanoparticle arrays.Comment: 4 pages, 3 figure
Electron Transport in Nanogranular Ferromagnets
We study electronic transport properties of ferromagnetic nanoparticle arrays
and nanodomain materials near the Curie temperature in the limit of weak
coupling between the grains. We calculate the conductivity in the Ohmic and
non-Ohmic regimes and estimate the magnetoresistance jump in the resistivity at
the transition temperature. The results are applicable for many emerging
materials, including artificially self-assembled nanoparticle arrays and a
certain class of manganites, where localization effects within the clusters can
be neglected.Comment: 4 pages, 2 figure
Fluctuoscopy of Disordered Two-Dimensional Superconductors
We revise the long studied problem of fluctuation conductivity (FC) in
disordered two-dimensional superconductors placed in a perpendicular magnetic
field by finally deriving the complete solution in the temperature-magnetic
field phase diagram. The obtained expressions allow both to perform
straightforward (numerical) calculation of the FC surface
and to get asymptotic expressions in
all its qualitatively different domains. This surface becomes in particular
non-trivial at low temperatures, where it is trough-shaped with . In this region, close to the
quantum phase transition,
is non-monotonic, in
agreement with experimental findings. We reanalyzed and present comparisons to
several experimental measurements. Based on our results we derive a qualitative
picture of superconducting fluctuations close to and T=0
where fluctuation Cooper pairs rotate with cyclotron frequency
and Larmor radius , forming some kind of quantum liquid with long coherence
length and slow relaxation
().Comment: 26 pages, 13 figures, 3 tables, RevTex 4.
Surface impedance of superconductors with magnetic impurities
Motivated by the problem of the residual surface resistance of the
superconducting radio-frequency (SRF) cavities, we develop a microscopic theory
of the surface impedance of s-wave superconductors with magnetic impurities. We
analytically calculate the current response function and surface impedance for
a sample with spatially uniform distribution of impurities, treating magnetic
impurities in the framework of the Shiba theory. The obtained general
expressions hold in a wide range of parameter values, such as temperature,
frequency, mean free path, and exchange coupling strength. This generality, on
the one hand, allows for direct numerical implementation of our results to
describe experimental systems (SRF cavities, superconducting qubits) under
various practically relevant conditions. On the other hand, explicit analytical
expressions can be obtained in a number of limiting cases, which makes possible
further theoretical investigation of certain regimes. As a feature of key
relevance to SRF cavities, we show that in the regime of "gapless
superconductivity" the surface resistance exhibits saturation at zero
temperature. Our theory thus explicitly demonstrates that magnetic impurities,
presumably contained in the oxide surface layer of the SRF cavities, provide a
microscopic mechanism for the residual resistance.Comment: 9 pages, 3 figs; v2: published versio
Dysbiosis of skin microbiota with increased fungal diversity is associated with severity of disease in atopic dermatitis
Background: Atopic dermatitis (AD) is a multifactorial inflammatory skin disease and an altered skin microbiota with an increase of Staphylococcus aureus has been reported. However, the role of fungi remains poorly investigated.
Objectives: We aimed to improve the understanding of the fungal skin microbiota, the mycobiota, in AD in relation to the bacterial colonization.
Methods: Skin swabs of 16 AD patients and 16 healthy controls (HC) from four different skin sites, that is antecubital crease, dorsal neck, glabella and vertex from multiple time points were analysed by DNA sequencing of the internal transcribed spacer region 1 (ITS1) and 16S rRNA gene for fungi and bacteria, respectively.
Results: Malassezia spp. were the predominant fungi in all subjects but with a decreased dominance in severe AD patients in favour of non-Malassezia fungi, for example Candida spp. For bacteria, a decrease of Cutibacterium spp. in AD patients in favour of Staphylococcus spp., particularly S. aureus, was observed. Further, both bacterial and fungal community compositions of severe AD patients significantly differed from mild-to-moderate AD patients and HC with the latter two having overall similar microbiota showing some distinctions in bacterial communities.
Conclusions: We conclude that severe AD is associated with a pronounced dysbiosis of the microbiota with increased fungal diversity. Potentially infectious agents, for example Staphylococcus and Candida, were increased in severe AD.
Keywords: atopic dermatitis; bacteria; disease severity; fungi; skin microbiot
Transport in Luttinger Liquids
We compute the transport properties of one dimensional interacting electrons,
also known as a Luttinger liquid. We show that a renormalization group study
allows to obtain the temperature dependence of the conductivity in an
intermediate temperature range. In this range the conductivity has a power-law
like dependence in temperature. At low temperatures, the motion proceed by
tunnelling between localized configurations. We compute this tunnelling rate
using a bosonization representation and an instanton technique. We find a
conductivity , where is the
temperature. We compare this results with the standard variable range hopping
(VRH) formula.Comment: Proceedings of the EURESCO Conference "Fondamental Problems of
Mesoscopic Physics", Granada, Spain (Sept. 2003), to be published by Kluwe
Large-scale quantum hybrid solution for linear systems of equations
State-of-the-art noisy intermediate-scale quantum devices (NISQ), although
imperfect, enable computational tasks that are manifestly beyond the
capabilities of modern classical supercomputers. However, present quantum
computations are restricted to exploring specific simplified protocols, whereas
the implementation of full-scale quantum algorithms aimed at solving concrete
large scale problems arising in data analysis and numerical modelling remains a
challenge. Here we introduce and implement a hybrid quantum algorithm for
solving linear systems of equations with exponential speedup, utilizing quantum
phase estimation, one of the exemplary core protocols for quantum computing. We
introduce theoretically classes of linear systems that are suitable for current
generation quantum machines and solve experimentally a -dimensional
problem on superconducting IBMQ devices, a record for linear system solution on
quantum computers. The considered large-scale algorithm shows superiority over
conventional solutions, demonstrates advantages of quantum data processing via
phase estimation and holds high promise for meeting practically relevant
challenges.Comment: 8 pages, 6 figure
- …