Two types arrays of ring half – wave and electrically small antennas (the typical sizes of the elements correspond to 1/10 of the wavelength) of SubTHz band with integrated Superconductor – Insulator – Normal metal – Insulator-Superconductor (SINIS) bolometers have been developed, fabricated and investigated. It is necessary to make numerical modeling of the full structure and to use additional reference channels in experimental studies for improving the accuracy of the spectral response estimations of receiving arrays. In this work, three reference channels were used for normalization: a pyroelectric receiver outside the cryostat and two cold channels – a RuO2 bolometer and chain of NIS junctions as a thermometer.

We have designed, fabricated, and experimentally studied a Superconductor-Insulator-Normal Metal-Insulator-Superconductor (SINIS) bolometer integrated in a twin-slot antenna with central frequency of 90 GHz and connected to a superconducting coplanar readout resonator. Such single pixel is intended for multichannel matrix of high-sensitive receiver for radioastronomy, in which readout of many channels is arranged via single coaxial cable instead of separate wires and separate amplifiers for each channel.

We analyzed the sensitivity of a separationless immunoassay scheme using functionalized magnetic nanoparticles (MNPs) and a sensitive HTS SQUID magnetometer. The signal of a 100 μL sample at a concentration of 1 mg/mL and field of 7.5 nT was 20 mΦ 0 . This makes it possible for the sensitivity to be within the range of 50 ng/mL at the required time of up to 100 s per a point in the frequency spectrum.

The problem of the fabrication of third-generation high-temperature superconductors (HTSCs) that are designed for the transmission of electric energy and the creation of nanoelectronic devices is studied in this work. The issues of the fabrication of dielectric substrates for the third generation wires are considered. The technology of HTSC film deposition on the quartz substrates is presented. Complex studies of sputtering of the buffer and superconducting YBa2Cu3O7 − δ (YBCO) layers were performed. The results of studies of electrophysical properties of the HTSC films on the quartz substrates are discussed.

The interplay between the quasi 1-dimensional CuO-chains and the 2-dimensional CuO2 planes of YBa2Cu3O6+x (YBCO) has been in focus for a long time. Although the CuO-chains are known to be important as charge reservoirs that enable superconductivity for a range of oxygen doping levels in YBCO, the understanding of the dynamics of its temperature-driven metal-superconductor transition (MST) remains a challenge. We present a combined study using x-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) revealing how a reconstruction of the apical O(4)-derived interplanar orbitals during the MST of optimally doped YBCO leads to substantial hole-transfer from the chains into the planes, i.e. self-doping. Our ionic model calculations show that localized divalent charge-transfer configurations are expected to be abundant in the chains of YBCO. While these indeed appear in the RIXS spectra from YBCO in the normal, metallic, state, they are largely suppressed in the superconducting state and, instead, signatures of Cu trivalent charge-transfer configurations in the planes become enhanced. In the quest for understanding the fundamental mechanism for high-T-c-superconductivity (HTSC) in perovskite cuprate materials, the observation of such an interplanar self-doping process in YBCO opens a unique novel channel for studying the dynamics of HTSC.

SrTiO3 is commonly used as a substrate for growth of various oxide films. Different reconstructions at the SrTiO3 surface have been claimed. A question is whether these survive subsequent depositions of thin films and influence film properties. Medium energy ion scattering (MEIS) was used to probe structure and composition of the surface layer of a TiO2-terminated (001) SrTiO3 single-crystal substrate and 1-4 unit cell (u.c.) thick LaMnO3 epilayers. Aligned spectra indicate enrichment of Ti at the surface and a TiO2 double-layer (DL) configuration. The DL arrangement survives pulsed-laser deposition of LaMnO3 in a background of high oxygen pressure (5 x 10(-2) mbar) while it is destroyed at lower oxygen pressure (10(-4) mbar). Simulations of random MEIS spectra indicate substantial interdiffusion and La doping of the substrate surface but all interfaces are nevertheless insulating. Copyright (C) EPLA, 2013

We show the influence of pulsed laser deposition fluence on the transport properties of the LaAlO(3)/SrTiO(3) (LAO/STO) heterointerface. Structural characterization by x-ray diffraction and medium energy ion spectrometry enables us to deduce that the electronic behaviour is extremely sensitive to the stoichiometry of the LAO layer as well as the structural quality of the STO surface. An optimum balance of these two quantities is demonstrated for an intermediate laser fluence.

Medium-energy ion spectroscopy (MEIS) has been used to study the depth profile and deduce the distribution of possible cationic substitutions in LaAlO3/SrTiO3 (LAO/STO) heterointerfaces. Analysis of La and Sr peaks in aligned and random MEIS spectra indicates that the surface layers of LAO on an STO substrate are not homogeneous and stoichiometric if the film thickness is less than 4 unit cell layers. This is possibly caused by a redistribution of La and Sr at the interface. Kelvin probe force microscopy reveals an inhomogeneous distribution of the surface potential in a 4 unit cell LAO film, indicating micrometer-sized regions of different compositions. Our findings provide a novel view on the microstructural origin of the electrically conductive interfaces.

We have re-assessed different methods to obtain single terminated perovskite oxide substrate surfaces of SrTiO3, LaAlO3 and NdGaO3. The surfaces have been probed by a combination of atomic and lateral force microscopy, X-ray photoelectron spectroscopy and reflection high-energy electron diffraction. (001)SrTiO3 surfaces were prepared with HF or plasma etching and annealing, (001)LaAlO3 surfaces were prepared with or without HCl etching and a consecutive annealing at 750–1100°C, and (110)NdGaO3 surfaces were only annealed. Two of the recipes have previously been suggested to result in A-site terminated surfaces. However, except for the case of high-temperature annealed LaAlO3 where we observe a double-terminated surface, our data suggest that the single terminated surfaces obtained by these methods were of B-site type.

The possibility of preparing bicrystalline Josephson junctions and bolometers based on superconducting MgB 2 on specially prepared bicrystalline MgO substrates is investigated. Microbridges 0.85–6.00 μm in width, intersecting the bicrystalline interface, are formed in epitaxial bicrystalline MgB 2 films grown on these substrates. It is found that annealing of bicrystalline samples in oxygen leads to a systematic decrease in the critical current, an increase in the temperature width of the superconducting transition region, and to an improvement of the current-voltage ( IV ) characteristic, which becomes close in shape to the IV characteristic of a Josephson junction. The response of such a junction to radiation at a frequency of 110 GHz with an amplitude attaining 0.5 mV is measured.

An optimized picoamperemeter based on a superconducting quantum interferometer device (SQUID) for a metal cold-electron bolometer is fabricated and experimentally studied. The intrinsic SQUID current noise caused by the input coil is estimated to be less than 1 pA/Hz1/2. Owing to the application of modulation electronics, current sensitivity in the input coil reaches 5 pA/Hz1/2 in the frequency band from 10 Hz to 10 kHz.

Measurement of the noises in mesoscopic conductors makes it possible to study the mechanisms of electron-electron and electron-phonon interaction in thin metal films. Depending on the ratio of the conductor dimensions and the characteristic lengths in metal, the dependence of the noises on the bias voltage can demonstrate passage from thermal noise to suppressed shot noise. Bridges made of chromium films are studied at temperatures ranging from 0.26 to 300 K. The I-V characteristics of such structures are linear within the entire temperature range, and the superconductor-normal metal junctions represent Andreev contacts at temperatures below the superconducting transition temperature of aluminum T-c = 1.2 K. In contrast to the tunnel junctions demonstrating a characteristic linear increase in the noises in accordance with the Schottky formula, the structures under study exhibit suppressed current noise.

A femtoamperemeter based on a superconducting quantum interference device (SQUID) with a planar on-chip gradiometric transformer and an additional volume cryogenic transformer on a toroidal ferromagnetic core is developed, fabricated, and experimentally studied. The conditions for the optimum matching of the SQUID to the signal source are analyzed. It is demonstrated that the conditions for the optimum matching and high coupling coefficient are satisfied in the transformer with a ferromagnetic core. The excess noise introduced by the core is studied experimentally. It is shown that double shielding using superconducting and ferromagnetic shields makes it possible to lower the cutoff frequency of the excess noise to less than I kHz.

Normal-metal hot-electron bolometers, each of which contains two superconductor-insulator-normal metal (SIN) junctions for electron cooling and two SIN junctions for temperature measurements, were fabricated and experimentally studied. The electron cooling by SIN junctions is an analog of the Peltier effect and allows one to reduce the effective electron temperature of a bolometer. The electron temperature was determined from the ratio of the differential resistance to normal one for several values of a constant bias. At a phonon temperature of 250 mK, the resistance ratio at zero bias reached 1000, which was close to the theoretical value for an ideal SIN junction. A decrease in the electron temperature from 250 to 90 mK was obtained.

A scanning HTS SQUID microscope for magnetic imaging samples at room temperature and atmospheric pressure has been developed. A sensor for the microscope was completed by a bicrystal dc SQUID and a needle made of soft magnetic material, which serves as a magnetic flux guide (MFG). This sensor has allowed magnetic imaging of the warm samples with spatial resolution of the order of 100 μm. Line scans of magnetic field produced by the current-carrying wires are measured and compared with results of a numerical modeling. The influence of the MFG on the image details has been studied.

We have developed a technological process for fabrication of YBa2Cu3Ox (YBCO) submicron wide Josephson junctions (JJ) on bicrystal substrates. This process is based on e-beam lithography and ion beam etching of YBCO films through carbon masks. A series of JJ with 0.4–1 μm width have been fabricated on SrTiO3 bicrystal substrates with misorientation angles θ=24° and 36.8° using this process. The analysis of the current–voltage characteristics of the fabricated junctions at high bias currents supports the model of electrons tunneling through the localized states (LS) formed in the barrier region. The approximation of experimental data on white noise of the junctions by theoretical formula, which represents the contribution of thermal noise as well as shot noise, shows that tunnel mechanism of electrons transport through the LS greatly dominates a normal metallic one.

An experimental investigation of high-temperature dc SQUID amplifier connected in series with a high-Tc superconductor (HTS) thin-film band-pass filter is presented. The SQUID amplifiers are designed with microstrip input coils and fabricated on bicrystal substrates of zirconia and sapphire with different misorientation angles of 24° and 37°. SQUID parameters are optimized to attain 50-Ω input impedance for the 1500 MHz central frequency range. The maximum power gain of the amplifier with six turn input coil was measured to be 6 dB at 800 MHz and 4.5 dB at 1750 MHz. Thin-film HTS YBCO filters are based on a band-pass quasi-elliptic prototype consisting of a set of parallel tank circuits connected to a shunt and separated by admittance inverters. The central frequency of the band-pass filter was adjusted close to 1750 MHz amplifier frequency with 4% bandwidth. The natural combination of a high-Tc SQUID amplifier with a HTS band-pass filter allows the reduction of out-of-band noise and optimization of amplifier performance, and demonstrates compatibility with practical components of front-end receiver subsystems.

Magnetic properties of a permalloy needle designed for use in a high-spatial-resolution scanning SQUID magnetic microscope as magnetic flux guide have been examined. The distributions of magnetic field normal component over a needle were imaged at 77 K in various applied magnetic fields. Influences of flux guide on the high temperature superconducting de SQUID characteristics have been superconducting investigated.