Universal Distribution of Transparencies in Highly Conductive Nb/AlOx/Nb Junctions (original) (raw)

Critical current in Nb-Cu-Nb junctions with nonideal interfaces

We report on experimental studies of superconductor (Nb) -normal metal (Cu) -superconductor (Nb) junctions with dirty interfaces between the different materials. By using a set of simultaneously prepared samples, we investigated the thickness dependence as well as the temperature dependence of the critical currents in the junctions. Good agreement between the decay of the measured critical currents and theoretical calculations was obtained without any fitting parameters.

Josephson current in ballistic Nb/InAs/Nb highly transmissive junctions

2002

Highly transmissive ballistic junctions are demonstrated between Nb and the two-dimensional electron gas formed at an InAs/AlSb heterojunction. A reproducible fabrication protocol is presented yielding high critical supercurrent values. Current-voltage characteristics were measured down to 0.4 K and the observed supercurrent behavior was analyzed within a ballistic model in the clean limit. This investigation allows us to demonstrate an intrinsic interface transmissivity approaching 90%. The reproducibility of the fabrication protocol makes it of interest for the experimental study of InAs-based superconductor-semiconductor hybrid devices. * Electronic address: giazotto@sns.it

Induced change of critical current density profile in Nb/Al-AlOx/Nb Josephson junctions

Journal of Physics: Conference Series, 2014

A technique to induce spatial modulation of critical current density in niobium based Josephson devices by using a selective thermal annealing is reported. By depositing a carbon film onto selected region of the Josephson element it is possible to induce a localized heating, with a spatial resolution less than 1µm, exploiting the much higher absorbance coefficient of carbon than the niobium one. The effectiveness of such technique is demonstrated by experimental measurement of the critical current vs. magnetic field, measured at T = 4.2 K, showing that the change of critical current density occurs only in the region corresponding to the absorber film area. Furthermore, the theoretical behaviour, by modelling a suitable step-like junction barrier shape, has been carried out to fit the experimental data in order to verify the selective modulation of critical current. This technique can be very useful in view of quantum computing experiments, Majorana fermions detection and superconducting magnetic sensors.

Josephson Current in Nb/InAs/Nb Highly Transmissive Ballistic Junctions

Journal of Superconductivity, 2000

Highly transmissive ballistic junctions are demonstrated between Nb and the two-dimensional electron gas formed at an InAs/AlSb heterojunction. A reproducible fabrication protocol is presented yielding high critical supercurrent values. Current-voltage characteristics were measured down to 0.4 K and the observed supercurrent behavior was analyzed within a ballistic model in the clean limit. This investigation allows us to demonstrate an intrinsic interface transmissivity approaching 90%. The reproducibility of the fabrication protocol makes it of interest for the experimental study of InAs-based superconductor-semiconductor hybrid devices. * Electronic address: giazotto@sns.it

Manifestation of coherent effects in the conductivity of superconductor/insulator/normal-metal/insulator/superconductor junctions

2003

An experimental and theoretical study is presented of coherent effects in electron transport in the doublebarrier SINIS junctions ͑where S, I, and N denote a superconductor, insulator, and normal metal, respectively͒. The appearance of a steplike subgap structure in the current-voltage characteristics of the Nb/Al/AlO x /Al/AlO x /Al/Nb superconducting junctions at a voltage Vϳ⌬ Nb /e ͑where ⌬ Nb is the superconducting energy gap of Nb͒ is interpreted as a manifestation of a nonequilibrium supercurrent at finite dc bias voltage ͑Finite-Bias Josephson Effect͒. The origin of this effect lies in the energy-band structure associated with a set of macroscopic quantum states characteristic of a SINIS junction. Specifically, the junction can have an energy level near energy ⌬ Nb , which provides an additional channel for dc Josephson current at V ϳ⌬ Nb /e. In addition, sharp features in the conductivity at a voltage near the gap-sum voltage were observed in both SINIS and SINININIS junctions, implying correlated quasiparticle tunneling in multiple-barrier junctions. Our theoretical model provides a good qualitative description of the quasiparticle conductivity, including narrow peaks at finite voltage and a zero-voltage anomaly observed on some samples, and suggests an alternative explanation of a feature interpreted earlier as gap-difference feature associated with the tunneling extraction of quasiparticles from the middle Al layer.

Theory of Andreev reflection in junctions with iron-based high-Tc superconductors

Physical Review B, 2009

We construct a theory for low-energy quantum transport in normal|superconductor junctions involving the recently discovered iron-based high-Tc superconductors. We properly take into account both Andreev bound surface states and the complex Fermi surface topology in our approach, and investigate the signatures of the possible order parameter symmetries for the FeAs-lattice. Our results could be helpful in determining the symmetry of the superconducting state in the iron-pnicitide superconductors. PACS numbers: 74.20.Rp, 74.50.+r, 74.70.Dd Introduction. Very recently, a family of iron-based superconductors with high transition temperatures was discovered, with a concomitant avalanche of both experimental and theoretical activity. . The highest T c measured so far in this class of materials is 55 K, and many experimental reports indicate signatures of unconventional superconducting pairing. However, it remains to be clarified what the exact symmetry is for both the orbital-and spin-part of the Cooper pair wavefunction -there has for instance been reports of both nodal 11 and fully gapped 10 order parameters (OPs) in the literature up to now.

Andreev reflection observation in Nb/FeSi/Nb and Nb/FeSi/Si/Nb Josephson junctions

Electrical properties of Josephson junctions Nb/FeSi/Nb with superconductor/ferromagnet (S/F)interfaces are presented. Due to Andreev reflection the nearly exact quadruple enhancement of the tunnel junction differential conductance compared with that of the normal state was achieved. The transparency of the S/F interfaces in our junctions was estimated to be close to unity. This almost ideal value is obtained due to the use of a very smooth amorphous magnetic FeSi alloy for the barrier preparation. The real structure of the Nb/FeSi/Nb tunnel junction is described as a S/F/I/F/S junction. Also Nb/FeSi/Si/Nb Josephson junctions were investigated and the results found on these junctions confirm the effects observed in Nb/FeSi/Nb.