Shot noise in superconducting junctions with weak link formed by Anderson impurity

A theory is developed to study shot noise in superconducting (SAS) and hybrid (SAN) junctions with singly occupied Anderson impurity (A) as a weak link. The zero-frequency DC component of the shot noise spectral density is calculated at zero temperature as a function of the bias at different Coulomb repulsion strengths U, and show a remarkable structure resulting from combination of electron-electron interaction and Andreev reflections.Comment: 4 two column pages including 4 .eps figure

Subgap anomaly and above-energy-gap structure in chains of diffusive SNS junctions

We present the results of low-temperature transport measurements on chains of superconductor--normal-constriction--superconductor (SNS) junctions fabricated on the basis of superconducting PtSi film. A comparative study of the properties of the chains, consisting of 3 and 20 SNS junctions in series, and single SNS junctions reveals essential distinctions in the behavior of the current-voltage characteristics of the systems: (i) the gradual decrease of the effective suppression voltage for the excess conductivity observed at zero bias as the quantity of the SNS junctions increases, (ii) a rich fine structure on the dependences dV/dI-V at dc bias voltages higher than the superconducting gap and corresponding to some multiples of 2\Delta/e. A model to explain this above-energy-gap structure based on energy relaxation of electron via Cooper-pair-breaking in superconducting island connecting normal metal electrods is proposed.Comment: RevTex, 5 pages, 4 figure

Nonlocal effects in the shot noise of diffusive superconductor - normal-metal systems

A cross-shaped diffusive system with two superconducting and two normal electrodes is considered. A voltage $eV < \Delta$ is applied between the normal leads. Even in the absence of average current through the superconducting electrodes their presence increases the shot noise at the normal electrodes and doubles it in the case of a strong coupling to the superconductors. The nonequilibrium noise at the superconducting electrodes remains finite even in the case of a vanishingly small transport current due to the absence of energy transfer into the superconductors. This noise is suppressed by electron-electron scattering at sufficiently high voltages.Comment: 4 pages, RevTeX, 2 eps figure

Multiple Andreev Reflection and Giant Excess Noise in Diffusive Superconductor/Normal-Metal/Superconductor Junctions

We have studied superconductor/normal metal/superconductor (SNS) junctions consisting of short Au or Cu wires between Nb or Al banks. The Nb based junctions display inherent electron heating effects induced by the high thermal resistance of the NS boundaries. The Al based junctions show in addition subharmonic gap structures in the differential conductance dI/dV and a pronounced peak in the excess noise at very low voltages V. We suggest that the noise peak is caused by fluctuations of the supercurrent at the onset of Josephson coupling between the superconducting banks. At intermediate temperatures where the supercurrent is suppressed a noise contribution ~1/V remains, which may be interpreted as shot noise originating from large multiple charges.Comment: 7 pages, 7 figures, extended versio

The role of the voluntary, community and social enterprise sector in Early Help: Critical reflections from embedded social care research

This is the final version. Available on open access from Wiley via the DOI in this recordData availability statement: The data that support the findings of this study are available on request from the corresponding author, Thomas El-Hoss. The data are not publicly available due to their containing sensitive information that could compromise the privacy of research participants.The independent review of children's social care (2022) has proposed a radical reset of England's children's services, shifting a remote, assessment heavy system towards one that works alongside communities to help prevent statutory interventions. However, notions around the harnessing of community resources to deliver Early Help are often underpinned by assumptions regarding the voluntary, community and social enterprise (VCSE) sector and the ease with which such organizations can be integrated into preventative strategies. This paper reports findings from embedded research within a unitary authority in Southwest England during remodelling of its Early Help service to work more collaboratively with local VCSE organizations. The study generated data from ethnographic observations, semi-structured interviews and focus groups with 95 participants, including local parents, service providers, VCSE organizations and Council leaders. The findings illustrate that families value the compassionate, responsive and flexible support available within many VCSE settings. However, differences in practice cultures, regulatory pressures on statutory providers, the need to (re)build trust in communities and sensitivities around power-sharing and resourcing meant negotiating VCSE sector integration was fraught with complexities. Few studies have gained such privileged access to a Local Authority's remodelling of Early Help services, and this paper has significant insights for the debates surrounding the independent review of children's social care (2022) and its recommendation to bring services ‘closer to communities’.Torbay Medical Research Fun

Child protection and family support: Experiences in a seaside resort

This is the final version. Available on open access from Elsevier via the DOI in this recordData availability: The data that has been used is confidential.Effective Early Help services are key to halting rising rates of children in care in the UK. Yet despite family support and child welfare interventions being unequally distributed across the country, the role of ‘place’ has received limited attention in the children’s social care arena. This paper examines the connections between coastal challenges, Early Help and child welfare interventions, drawing on embedded research undertaken within a Local Authority on England’s coast with elevated levels of children in care. We focus on families’ experiences raising children in a seaside resort area as well as professionals’ perspectives on the place-based challenges faced delivering effective and accessible Early Help support. The study generated data from ethnographic observations, semi-structured interviews, and focus groups with local parents/carers (n = 57), service managers and frontline professionals (n = 14), and the Voluntary, Community, and Social Enterprise (VCSE) sector (n = 22). The findings highlight how the socio-economic challenges associated with many seaside resort areas, including housing pressures, a seasonal and low-wage economy, and the transience of the population, present difficulties for parents/carers in raising and supporting their children. For professionals delivering Early Help, high levels of housing instability, elevated inward migration, resource constraints and challenges around recruitment and retention presented challenges to delivering services. This paper recommends increased emphasis in regulation and resourcing around family support that considers the spatial and geographic dynamics that influence the incidence, structuring, and experiences of child and family welfare.Torbay Medical Support FundWellcome Centre for Cultures and Environments of HealthNational Institute for Health and Care Research (NIHR

Two-dimensional array of diffusive SNS junctions with high-transparent interfaces

We report the first comparative study of the properties of two-dimensional arrays and single superconducting film - normal wire - superconducting film (SNS) junctions. The NS interfaces of our SNS junctions are really high transparent, for superconducting and normal metal parts are made from the same material (superconducting polycrystalline PtSi film). We have found that the two-dimensional arrays reveal some novel features: (i) the significant narrowing of the zero bias anomaly (ZBA) in comparison with single SNS junctions, (ii) the appearance of subharmonic energy gap structure (SGS), with up to n=16 (eV=\pm 2\Delta/n), with some numbers being lost, (iii) the transition from 2D logarithmic weak localization behavior to metallic one. Our experiments show that coherent phenomena governed by the Andreev reflection are not only maintained over the macroscopic scale but manifest novel pronounced effects as well. The behavior of the ZBA and SGS in 2D array of SNS junctions strongly suggests that the development of a novel theoretical approach is needed which would self-consistently take into account the distribution of the currents, the potentials, and the superconducting order parameter.Comment: RevTex, 5 pages, 5 figure

Coherent low-energy charge transport in a diffusive S-N-S junction

We have studied the current voltage characteristics of diffusive mesoscopic Nb-Cu-Nb Josephson junctions with highly-transparent Nb-Cu interfaces. We consider the low-voltage and high-temperature regime eV<\epsilon_{c}<k_{B}T where epsilon_{c} is the Thouless energy. The observed excess current as well as the observed sub-harmonic Shapiro steps under microwave irradiation suggest the occurrence of low-energy coherent Multiple Andreev Reflection (MAR).Comment: 4 pages, 4 figures, final versio

Full Current Statistics in Diffusive Normal-Superconductor Structures

We study the current statistics in normal diffusive conductors in contact with a superconductor. Using an extension of the Keldysh Green's function method we are able to find the full distribution of charge transfers for all temperatures and voltages. For the non-Gaussian regime, we show that the equilibrium current fluctuations are enhanced by the presence of the superconductor. We predict an enhancement of the nonequilibrium current noise for temperatures below and voltages of the order of the Thouless energy E_Th=D/L^2. Our calculation fully accounts for the proximity effect in the normal metal and agrees with experimental data. We demonstrate that the calculation of the full current statistics is in fact simpler than a concrete calculation of the noise.Comment: 4 pages, 2 figures (included

Current noise in long diffusive SNS junctions in the incoherent MAR regime

Spectral density of current fluctuations at zero frequency is calculated for a long diffusive SNS junction with low-resistive interfaces. At low temperature, T << Delta, the subgap shot noise approaches linear voltage dependence, S=(2/ 3R)(eV + 2Delta), which is the sum of the shot noise of the normal conductor and voltage independent excess noise. This result can also be interpreted as the 1/3-suppressed Poisson noise for the effective charge q = e(1+2Delta/eV) transferred by incoherent multiple Andreev reflections (MAR). At higher temperatures, anomalies of the current noise develop at the gap subharmonics, eV = 2Delta/n. The crossover to the hot electron regime from the MAR regime is analyzed in the limit of small applied voltages.Comment: improved version, to be published in Phys. Rev.