Nonequilibrium phenomena in planar Josephson SNS nanostructures, where the superconductor (S) is Nb and the normal metal (N) is Cu or Au, have been studied experimentally. Using additional N electrodes attached to the S banks of the Josephson SNS junction, transport measurements have been performed at low temperatures with the injection of quasiparticles with the use of local and nonlocal connection schemes. The charge-imbalance relaxation length in niobium at temperatures much lower than the superconducting transition temperature has been determined experimentally for the first time.

A nonmonotonic dependence of the critical Josephson supercurrent on the injection current through a normal metal/ferromagnet weak link from a single domain ferromagnetic strip has been observed experimentally in nanofabricated planar crosslike S-N/F-S Josephson structures. This behavior is explained by 0-pi and pi-0 transitions, which can be caused by the suppression and Zeeman splitting of the induced superconductivity due to interaction between N and F layers, and the injection of spin-polarized current into the weak link. A model considering both effects has been developed. It shows the qualitative agreement between the experimental results and the theoretical model in terms of spectral supercurrent-carrying density of states of S-N/F-S structure and the spin-dependent double-step nonequilibrium quasiparticle distribution.

An analytical approach that makes it possible to reconstruct the current–phase relation (CPR) in Josephson structures included in one of the arms of a two-junction superconducting quantum interference device (SQUID), where the second junction has a significantly higher critical current and a known (sinusoidal) CPR, has been developed. The developed methods of analytical and numerical studies of current–flow transformations in two-junction SQUIDs make it possible to reconstruct the CPR of a junction with a low critical current taking into account both the existence of the self-inductance of the interferometer contour and a possible asymmetry in the supply current system. The efficiency of this approach has been confirmed by the experimental study of niobium–aluminum/aluminum oxide–niobium test structures with the known CPR.

We report on the Shubnikov-de Haas oscillations in the longitudinal resistance of thin films of three-dimensional topological insulator Sb2Te3 grown by means of molecular beam epitaxy. The oscillations persist up to the temperatures of 30 K, and the measurements at various tilt angles reveal that they originate from a two-dimensional system. Using a top gate, we further study the change of oscillation amplitude and frequency, which in combination with the standard Hall measurements suggest the origin of oscillations to be at the interface between the film and the Si substrate. Published by AIP Publishing.

We investigate the proximity effect in InAs nanowire (NW) junctions with superconducting contacts made of Al. The carrier density in InAs is tuned by means of the back gate voltage V-g. At high positive V-g the devices feature transport signatures characteristic of diffusive junctions with highly transparent interfaces-sizable excess current, re-entrant resistance effect and proximity gap values (Delta(N)) close to the Al gap (Delta(0)). At decreasing V-g, we observe a reduction of the proximity gap down to Delta(N) approximate to Delta(0)/2 at NW conductances similar to 2 e(2) h(-1), which is interpreted in terms of carrier density dependent reduction of the Al/InAs interface transparency. We demonstrate that the experimental behavior of Delta(N) is closely reproduced by a model with rectangular potential barrier at the Al/InAs interface.

We present a microscopic theory of the superconducting proximity effect in a semiconducting thin film with spin-orbit interaction (N_SO) in an external magnetic field. We demonstrate that an effective 1D Hamiltonian which describes induced superconductivity in N_SO in contact with a usual s-wave superconductor possesses not only spin-singlet induced superconducting order parameter term, as commonly adopted, but spin triplet order parameter term also. Using this new effective Hamiltonian we confirm previous results for a normal current across contacts of N_SO with a normal metal and for a Josephson current with the same N_SO with induced superconductivity, obtained previously in the framework of the phenomenological Hamiltonian without spin-triplet terms. However, a calculated current-phase relation across the transparent contact between N_SO with induced superconductivity in magnetic field and usual s-wave superconductor differs significantly from previous results. We suggest the experiment which can confirm our theoretical predictions.

Ternary (Bi1-xSbx)2Te3 films with an Sb content between 0 and 100% were deposited on a Si(111) substrate by means of molecular beam epitaxy. X-ray diffraction measurements confirm single crystal growth in all cases. The Sb content is determined by X-ray photoelectron spectroscopy. Consistent values of the Sb content are obtained from Raman spectroscopy. Scanning Raman spectroscopy reveals that the (Bi1-xSbx)2Te3 layers with an intermediate Sb content show spatial composition inhomogeneities. The observed spectra broadening in angular-resolved photoemission spectroscopy (ARPES) is also attributed to this phenomena. Upon increasing the Sb content from x=0 to 1 the ARPES measurements show a shift of the Fermi level from the conduction band to the valence band. This shift is also confirmed by corresponding magnetotransport measurements where the conductance changes from n- to p-type. In this transition region, an increase of the resistivity is found, indicating a location of the Fermi level within the band gap region. More detailed measurements in the transition region reveals that the transport takes place in two independent channels. By means of a gate electrode the transport can be changed from n- to p-type, thus allowing a tuning of the Fermi level within the topologically protected surface states.

Nonlocal supercurrent was observed in mesoscopic planar SNS Josephson junction with additional normal metal electrodes when nonequilibrium quasiparticles were injected from the normal metal electrode in one of the superconducting banks of the Josephson junction in the absence of net transport current through the junction. We claim that the effect observed is due to a supercurrent counterflow appearing to compensate the quasiparticle flow in the SNS weak link. We have measured SNS junction response for different distances from the quasiparticle injector to the SNS junction at temperatures far below the superconducting transition temperature. The charge-imbalance relaxation length was estimated by using modified Kadin, Smith and Skocpol scheme in the case of planar geometry. The model developed allows to describe the interplay of the charge imbalance and Josephson effects in the nanoscale proximity system in detail.

We report on the fabrication and characterization of symmetric nanowire-based Josephson junctions, that is, Al- and Nb-based junctions, and asymmetric junctions employing superconducting Al and Nb. In the symmetric junctions, a clear and pronounced Josephson supercurrent is observed. These samples also show clear signatures of subharmonic gap structures. At zero magnetic field, a Josephson coupling is found for the asymmetric Al/InAs-nanowire/Nb junctions as well. By applying a magnetic field above the critical field of Al or by raising the temperature above the critical temperature of Al the junction can be switched to an effective single-interface superconductor/nanowire structure. In this regime, a pronounced zero-bias conductance peak due to reflectionless tunneling has been observed.

We used InAs nanowires with two different charge carrier concentration to fabricate Josephson junctions with superconducting Nb electrodes. For highly doped nanowire junctions a supercurrent is observed up to T similar to 5 K, for low doped nanowire junctions we were able to tune the Josephson current by a back gate voltage. Owing to the transparent interface between Nb and InAs nanowires subharmonic gap structures due to multiple Andreev reflection have been observed. Furthermore, the effect of magnetic field on the Josephson current was investigated and a monotonous decrease of Josephson current was found. The observed behavior has been compared with a theoretical model.

Specific features of the proximity effect and Josephson behavior of submicron planar SNS junctions fabricated by electron beam lithography and shadow evaporation have been studied experimentally and theoretically. The critical current of the junctions has been found to drastically increase with a decrease in temperature, which is associated with a change in the effective size of the weak link owing to the additional SN interface.

We have investigated the differential resistance of hybrid planar Al-(Cu/Fe)-Al submicron bridges at low temperatures and in weak magnetic fields. The structure consists of a Cu/Fe bilayer forming a bridge between two superconducting Al electrodes. In the superconducting state of Al electrodes, we have observed a double-peak peculiarity in differential resistance of the S-(N/F)-S structures at a bias voltage corresponding to the minigap. We claim that this effect (the splitting of the minigap) is due to an electron spin polarization in the normal metal which is induced by the ferromagnet. We have demonstrated that the double-peak peculiarity is converted to a single peak at a coercive applied field corresponding to zero magnetization of the Fe layer.

We report on the fabrication and measurements of planar mesoscopic Josephson junctions formed by InAs nanowires coupled to superconducting Nb terminals. The use of Si-doped InAs-nanowires with different bulk carrier concentrations allowed to tune the properties of the junctions. We have studied the junction characteristics as a function of temperature, gate voltage, and magnetic field. For junctions with high doping concentrations in the nanowire, Josephson supercurrent values up to 100 nA are found. Owing to the use of Nb as superconductor, the Josephson coupling persists at temperatures up to 4 K. In all junctions, the critical current monotonously decreased with the magnetic field, which can be explained by a recently developed theoretical model for the proximity effect in ultra-small Josephson junctions. For the low-doped Josephson junctions, a control of the critical current by varying the gate voltage has been demonstrated. We have studied conductance fluctuations in nanowires coupled to superconducting and normal metal terminals. The conductance fluctuation amplitude is found to be about 6 times larger in superconducting contacted nanowires. The enhancement of the conductance fluctuations is attributed to phase-coherent Andreev reflection as well as to the large number of phase-coherent channels due to the large superconducting gap of the Nb electrodes.

The microstructures of thin coating films of pure palladium and palladium alloys deposited from organic electrolytes onto different metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005–1μm thick films with high adhesive strength to the substrate surface. X-ray spectral analysis, X-ray phase analysis, transmission and scanning electron microscopy were used to determine the composition and structure of alloy coatings of binary systems: Pd–Au, Pd–Ag, Pd–Ni, Pd–Pb, and ternary system Pd–Au–Ni. The coatings of Pd–Au, Pd–Ag, and Pd–Ni have a solid solution structure, whereas Pd–Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11–35nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed.

We experimentally studied the Josephson supercurrent in Nb/InN-nanowire/Nb junctions. Large critical currents up to 5.7 $\mu$A have been achieved, which proves the good coupling of the nanowire to the superconductor. The effect of a magnetic field perpendicular to the plane of the Josephson junction on the critical current has been studied. The observed monotonous decrease of the critical current with magnetic field is explained by the magnetic pair-breaking effect in planar Josephson junctions of ultra-narrow width [J. C. Cuevas and F. S. Bergeret, Phys. Rev. Lett. 99, 217002 (2007)]