2,817 research outputs found
Functional renormalization group study of the Anderson--Holstein model
We present a comprehensive study of the spectral and transport properties in
the Anderson--Holstein model both in and out of equilibrium using the
functional renormalization group (FRG). We show how the previously established
machinery of Matsubara and Keldysh FRG can be extended to include the local
phonon mode. Based on the analysis of spectral properties in equilibrium we
identify different regimes depending on the strength of the electron--phonon
interaction and the frequency of the phonon mode. We supplement these
considerations with analytical results from the Kondo model. We also calculate
the non-linear differential conductance through the Anderson--Holstein quantum
dot and find clear signatures of the presence of the phonon mode.Comment: 19 pages, 8 figure
Physics of Proximity Josephson Sensor
We study the proximity Josephson sensor (PJS) in both bolometric and
calorimetric operation and optimize it for different temperature ranges between
25 mK and a few Kelvin. We investigate how the radiation power is absorbed in
the sensor and find that the irradiated sensor is typically in a weak
nonequilibrium state. We show in detail how the proximity of the
superconductors affects the device response: for example via changes in
electron-phonon coupling and out-of-equilibrium noise. In addition, we estimate
the applicability of graphene as the absorber material.Comment: 13 pages, 11 figures, submitted to Journal of Applied Physics, v2:
Addition of a new section discussing the radiation coupling to the device,
several minor change
Theory of temperature fluctuation statistics in superconductor-normal metal tunnel structures
We describe the statistics of temperature fluctuations in a SINIS structure,
where a normal metal island (N) is coupled by tunnel junctions (I) to two
superconducting leads (S). We specify conditions under which this structure
exhibits manifestly non-Gaussian fluctuations of temperature. We consider both
the Gaussian and non-Gaussian regimes of these fluctuations, and the current
fluctuations that are caused by the fluctuating temperature. We also describe a
measurement setup that could be used to observe the temperature fluctuations.Comment: 10 pages, 9 figures, final versio
Fully Overheated Single-Electron Transistor
We consider the fully overheated single-electron transistor, where the heat
balance is determined entirely by electron transfers. We find three distinct
transport regimes corresponding to cotunneling, single-electron tunneling, and
a competition between the two. We find an anomalous sensitivity to temperature
fluctuations at the crossover between the two latter regimes that manifests in
an exceptionally large Fano factor of current noise.Comment: 6 pages, 3 figures, includes Appendi
Charge transport in ballistic multiprobe graphene structures
We study the the transport properties of multiterminal ballistic graphene
samples, concentrating on the conductance matrix, fluctuations and
cross-correlations. Far away from Dirac point, the current is carried mostly by
propagating modes and the results can be explained with the conventional
semiclassical picture familiar from ray optics, where electrons propagate along
a single direction before scattering or reaching the terminals. However, close
to the Dirac point the transport is due to evanescent modes which do not have
to follow a rectilinear path. As we show in this Letter, this property of the
evanescent modes influences the conductance matrix. However, at best it can be
observed by measuring the cross correlations in an exchange Hanbury Brown-Twiss
experiment.Comment: 5 pages, 5 figure
Nonequilibrium characteristics in all-superconducting tunnel structures
We study the nonequilibrium characteristics of superconducting tunnel
structures in the case when one of the superconductors is a small island
confined between large superconductors. The state of this island can be probed
for example via the supercurrent flowing through it. We study both the
far-from-equilibrium limit when the rate of injection for the electrons into
the island exceeds the energy relaxation inside it, and the quasiequilibrium
limit when the electrons equilibrate between themselves. We also address the
crossover between these limits employing the collision integral derived for the
superconducting case. The clearest signatures of the nonequilibrium limit are
the anomalous heating effects seen as a supercurrent suppression at low
voltages, and the hysteresis at voltages close to the gap edge ,
resulting from the peculiar form of the nonequilibrium distribution function.Comment: 8 pages, 10 figure
Giant current fluctuations in an overheated single electron transistor
Interplay of cotunneling and single-electron tunneling in a thermally
isolated single-electron transistor (SET) leads to peculiar overheating
effects. In particular, there is an interesting crossover interval where the
competition between cotunneling and single-electron tunneling changes to the
dominance of the latter. In this interval, the current exhibits anomalous
sensitivity to the effective electron temperature of the transistor island and
its fluctuations. We present a detailed study of the current and temperature
fluctuations at this interesting point. The methods implemented allow for a
complete characterization of the distribution of the fluctuating quantities,
well beyond the Gaussian approximation. We reveal and explore the parameter
range where, for sufficiently small transistor islands, the current
fluctuations become gigantic. In this regime, the optimal value of the current,
its expectation value, and its standard deviation differ from each other by
parametrically large factors. This situation is unique for transport in
nanostructures and for electron transport in general. The origin of this
spectacular effect is the exponential sensitivity of the current to the
fluctuating effective temperature.Comment: 10 pages, 11 figure
Towards a Protocol for the Collection of VGI Vector Data
A protocol for the collection of vector data in Volunteered Geographic Information (VGI) projects is proposed. VGI is a source of crowdsourced geographic data and information which is comparable, and in some cases better, than equivalent data from National Mapping Agencies (NMAs) and Commercial Surveying Companies (CSC). However, there are many differences in how NMAs and CSC collect, analyse, manage and distribute geographic information to that of VGI projects. NMAs and CSC make use of robust and standardised data collection protocols whilst VGI projects often provide guidelines rather than rigorous data collection specifications. The proposed protocol addresses formalising the collection and creation of vector data in VGI projects in three principal ways: by manual vectorisation; field survey; and reuse of existing data sources. This protocol is intended to be generic rather than being linked to any specific VGI project. We believe that this is the first protocol for VGI vector data collection that has been formally described in the literature. Consequently, this paper shall serve as a starting point for on-going development and refinement of the protocol
Waterfalls as sources of small charged aerosol particles
In this study, we measured the mobility distributions of cluster and intermediate ions with an ion spectrometer near a waterfall. We observed that the concentration of negative 1.5–10 nm ions was one-hundred fold higher than a reference point 100 m away from the waterfall. Also, the concentration of positive intermediate ions was found to be higher than that at the reference point by a factor of ten. This difference was observed only at the smallest sizes; above 10 nm the difference was insignificant
Vacancy Defects In O-Doped Gan Grown By Molecular-Beam Epitaxy: The Role Of Growth Polarity And Stoichiometry
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