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The measurements of dc Josephson and quasiparticle current-voltage characteristics of four-layered Nb/Al-AlOx-Nb devices with a fixed Nb thickness of 270 nm and Al thicknesses ranging from 40 to 120 nm are reported and analyzed in the framework of a microscopic model developed to determine stationary properties of dirty limit double-barrier junctions. It is shown that the temperature dependence of the supercurrent as well as the values of characteristic voltages are well reproduced by the model calculations with only one fitting parameter. We have revealed a hysteretic-to-nonhysteretic transition in the current-voltage characteristics of our junctions at temperatures near 4.2 K and argue that this effect is caused by two factors: high-transparency insulating barrier with a broad distribution of the transmission coefficient and the temperature as a tuning parameter, which decreases the McCumber-Stewart parameter from values above unity at low temperatures to less than one above 4.2 K. Finally, we show how and why the temperature stability of the proposed Josephson devices can be significantly improved by choosing an appropriate Al thickness. [ABSTRACT FROM AUTHOR]

The Braess paradox encountered in classical user-optimized network system, such as a transportation network, is a counter intuitive phenomenon when the travel cost (time) for every user can be increased by adding a new road or, more generally, when the overall net performance can degrade after addition of an extra available choice. In this work, we discuss the possibility of a similar effect in a phase-coherent quantum transport and demonstrate it by example of a simple Y-shaped metallic fork. To reveal the Braess-like partial suppression of the charge flow in such device, it is proposed to transfer two outgoing arms into a superconducting state. We show that the differential conductance-vs. voltage spectrum of the hybrid fork structure varies considerably when the extra link between the two superconducting leads is added and it can serve as an indicator of quantum correlations which manifest themselves in the quantum Braess paradox. [ABSTRACT FROM AUTHOR]

We report the performance of a reliable three-dimensional nanometer-sized Superconducting QUantum Interference Device (SQUID). The use of superconductor-isolator-superconductor Nb/ Al-AlOx/Nb Josephson tunnel junctions together with small SQUID loop dimensions permits a high modulation depth of the SQUID’s critical current and thus leads to very low intrinsic flux noise of the device. In particular, we present electrical characterization including detailed noise investigations. At 4.2 K, two-stage noise measurements with a SQUID as a low noise preamplifier result in a white flux noise of 51 nφ0/Hz1/2, which is equivalent to an energy resolution of 1.3 h, with h being Planck’s constant. Simulation of spin sensitivities results in about 1 μB/Hz1/2 for an electron spin positioned directly above the SQUID ring. [ABSTRACT FROM AUTHOR]

Conventional Josephson metal-insulator-metal devices are inherently underdamped and exhibit hysteretic current-voltage response due to a very high subgap resistance compared to that in the normal state. At the same time, overdamped junctions with single-valued characteristics are needed for most superconducting digital applications. The usual way to overcome the hysteretic behavior is to place an external low-resistance normal-metal shunt in parallel with each junction. Unfortunately, such solution results in a considerable complication of the circuitry design and introduces parasitic inductance through the junction. This paper provides a concise overview of some generic approaches that have been proposed in order to realize internal shunting in Josephson heterostructures with a barrier that itself contains the desired resistive component. The main attention is paid to self-shunted devices with local weak-link transmission probabilities that are so strongly disordered in the interface plane that transmission probabilities are tiny for the main part of the transition region between two super-conducting electrodes, while a small part of the interface is well transparent. We discuss the possibility of realizing a universal bimodal distribution function and emphasize advantages of such junctions that can be considered as a new class of self-shunted Josephson devices promising for practical applications in superconducting electronics operating at 4.2 K. [ABSTRACT FROM AUTHOR]

We report a novel sensing method for fluorescence-labelled microRNAs (miRNAs) spotted on an all-dielectric photonic structure. Such a photonic structure provides an enhanced excitation and a directional beaming of the emitted fluorescence, resulting in a significant improvement of the overall signal collected. As a result, the Limit of Detection (LoD) is demonstrated to decrease by a factor of about 50. A compact read-out system allows a wide-field imaging-based detection, with little or no optical alignment issues, which makes this approach particularly interesting for further development for example in microarray-type bioassays. [ABSTRACT FROM AUTHOR]

Cylinder forming PS-b-PMMA block copolymer (BCP) thin films were deposited on pre-patterned surfaces with densely packed and nanometer wide trenches defined by conventional top down approaches and arranged to form a periodic grating. The films were subsequently annealed at 250 °C for times ranging from 30 s to 900 s in a rapid thermal processing device and their morphology evolution within the topographically defined structures was systematically investigated. Irrespective of the surface neutralization, an irreversible orientational flipping of the BCP microdomains inside the trenches was observed and attributed to de-swelling of the polymeric film as a consequence of a progressive desorption of the solvent retained inside the film. Systematic investigation of the annealing process indicates that the flipping is strongly dependent on the geometric parameters of the trenches and on the relative position of the analysed trench with respect to the periodic topographic structure. [ABSTRACT FROM AUTHOR]

The use of linear and circular subwavelength gratings for improving the fluorescence extraction from organic dyes spotted on the surface of a one-dimensional photonic crystal is demonstrated. The one-dimensional photonic crystal hosting the gratings allows Bloch surface waves (BSWs) to be coupled in the visible range. We provide experimental evidence for the distributed diffraction of BSW-coupled fluorescence that is locally excited using a microscope-based setup. By diffracting the BSW-coupled fluorescence, a significant improvement in the total fluorescence collection is obtained as compared to a flat one-dimensional photonic crystal. [ABSTRACT FROM AUTHOR]

We report low-temperature measurements of current-voltage characteristics for highly conductive Nb/Al-AlOx-Nb junctions with thicknesses of the Al interlayer ranging from 40 to 150 nm and ultrathin barriers formed by diffusive oxidation of the Al surface. In a superconducting state these devices have revealed a strong subgap current leakage. Analyzing Cooper-pair and quasiparticle currents across the devices, we conclude that the strong suppression of the subgap resistance compared with conventional tunnel junctions is not related to technologically derived pinholes in the barrier but rather has more fundamental grounds. We argue that it originates from a universal bimodal distribution of transparencies across the aluminum oxide barrier proposed earlier by Schep and Bauer (1997 Phys. Rev. Lett. 78 3015). We suggest a simple physical explanation of its source in the nanometer-thick oxide films relating it to strong local barrier-height fluctuations in the nearest to conducting electrode layers of the insulator which are generated by oxygen vacancies in thin aluminum oxide tunnel barriers formed by thermal oxidation. [ABSTRACT FROM AUTHOR]

The temperature dependence of the quantized voltage steps near the superconducting transition temperature of Nb/Al–AlOx/Nb overdamped Josephson junctions irradiated at 75 GHz has been studied. These junctions can switch between the hysteretic and nonhysteretic regime either by varying a fabrication parameter or, as shown in the present paper, by changing the junction operating temperature. Due to the high values of JC and VC up to 75 kA/cm2 and 0.5 mV at 4.2 K, respectively, and to the moderate temperature dependence of these parameters, the height of the first rf-induced step was larger than 1 mA at T=6–8 K, corresponding to 0.7–0.9T/TC on a junction of 5×5 μm2. The flatness at the nanovolt level of this step demonstrates the feasibility of programable or ac voltage standards operating in a cryocooler setup. [ABSTRACT FROM AUTHOR]

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper. [ABSTRACT FROM AUTHOR]

Monodisperse silica nanospheres with sizes ranging from 250 to 725 nm were prepared and assembled into monolayers to produce regularly distributed light hot spots at the surface of oxidized silicon substrates when illuminated by a laser. Single UV nanosecond laser pulses were employed with energies above the local ablation threshold for the silicon dioxide layer, resulting in the direct formation of 2D periodically porous membranes on top of the silicon. The periodicity of the array was driven by the size of the self-assembled nanospheres. While the local field enhancement was strongly dependent on the sphere size due to Mie resonances, the size and morphology of the produced features could be maintained for all tested situations by balancing the change in local fields with the laser pulse energy. This work demonstrates the fabrication of 90 nm thick porous membranes with pore size of about 100 nm and periodicity ranging from 250 to 725 nm. [ABSTRACT FROM AUTHOR]