Multiple Andreev reflections in diffusive SNS structures

We report new measurements on sup-gap energy structure originating from multiple Andreev reflections in mesoscopic SNS junctions. The junctions were fabricated in a planar geometry with high transparency superconducting contacts of Al deposited on highly diffusive and surface d-doped n++-GaAs. For samples with a normal GaAs region of active length 0.3um the Josephson effect with a maximal supercurrent Ic=3mA at T=237mK was observed. The sub-gap structure was observed as a series of local minima in the differential resistance at dc bias voltages V=2D/ne with n=1,2,4 i.e. only the even sub-gap positions. While at V=2D/e (n=1) only one dip is observed, the n=2, and the n=4 sub-gap structures each consists of two separate dips in the differential resistance. The mutual spacing of these two dips is independent of temperature, and the mutual spacing of the n=4 dips is half of the spacing of the n=2 dips. The voltage bias positions of the sub-gap differential resistance minima coincide with the maxima in the oscillation amplitude when a magnetic field is applied in an interferometer configuration, where one of the superconducting electrodes has been replaced by a flux sensitive open loop.Comment: 20 pages, 7 figure

Observation of supercurrent enhancement in SNS junctions by non-equilibrium injection into supercurrent carrying bound Andreev states

We report for the first time enhancement of the supercurrent by means of injection in a mesoscopic three terminal planar SNSNS device made of Al on GaAs. When a current is injected from one of the superconducting Al electrodes at an injection bias $V=\Delta(T)/e$, the DC Josephson current between the other two superconducting electrodes has a maximum, giving evidence for an enhancement due to a non-equilibrium injection into bound Andreev states of the underlying semiconductor. The effect persists to temperatures where the equilibrium supercurrent has vanished.Comment: 7 pages + 3 figures. Resubmitted to Phys. Rev. Lett. Contents change

Ion channel recordings on an injection-molded polymer chip

In this paper, we demonstrate recordings of the ion channel activity across the cell membrane in a biological cell by employing the so-called patch clamping technique on an injection-molded polymer microfluidic device. The findings will allow direct recordings of ion channel activity to be made using the cheapest materials and production platform to date and with the potential for very high throughput. The employment of cornered apertures for cell capture allowed the fabrication of devices without through holes and via a scheme comprising master origination by dry etching in a silicon substrate, electroplating in nickel and injection molding of the final part. The most critical device parameters were identified as the length of the patching capillary and the very low surface roughness on the inside of the capillary. The cross-sectional shape of the orifice was found to be less critical, as both rectangular and semicircular profiles seemed to have almost the same ability to form tight seals with cells with negligible leak currents. The devices were functionally tested using human embryonic kidney cells expressing voltage-gated sodium channels (Nav1.7) and benchmarked against a commercial state-of-the-art system for automated ion channel recordings. These experiments considered current–voltage (IV) relationships for activation and inactivation of the Nav1.7 channels and their sensitivity to a local anesthetic, lidocaine. Both IVs and lidocaine dose–response curves obtained from the injection-molded polymer device were in good agreement with data obtained from the commercial system