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We report on the dependence on field and temperature of the critical current of micro superconducting quantum interference devices (SQUIDs): SQUIDs with diameters as small as 1 µm using Dayem bridges as weak links. We model these SQUIDs by solving the Ginzburg-Landau equations with appropriate boundary conditions to obtain the supercurrent-phase relationships. These solutions show that the phase drops and depression of the order parameter produced by supercurrent flow are often distributed throughout the micro-SQUID structure, rather than being localized in the bridge area, for typical micro-SQUID geometries and coherence lengths. The resultant highly nonsinusoidal current-phase relationships I[sub c](ψ) lead to reduced modulation depths and triangular dependences of the micro-SQUID critical currents on applied magnetic flux I[sub c](φ). Our modeling agrees well with our measurements on both Al and Nb micro-SQUIDs. [ABSTRACT FROM AUTHOR]

Presents a study which conducted a noise spectroscopy of semiconductor deep level centers in gallium arsenide-aluminum[sub x]gallium[sub 1-x]arsenide heterostructures. Description of the model; Experiment; Results and discussion.

Discusses a study on electron heating in silicon dioxide and off-stoichiometric silicon dioxide films. Details on experimental techniques used in the study; Demonstration of the gradual heating of electronic carrier distributions; Treatment of the relationship of electron heating to electron trapping, positive charge generation, interface state creation and dielectric breakdown.

We have designed and characterized a micro-SQUID with dispersive readout for use in low temperature scanning probe microscopy systems. The design features a capacitively shunted RF SQUID with a tunable resonance frequency from 5 to 12 GHz, micrometer spatial resolution, and integrated superconducting coils for local application of magnetic fields. The SQUID is operated as a nonlinear oscillator with a flux- and power-dependent resonance frequency. Measurements for device characterization and noise benchmarking were carried out at 4 K. The measured flux noise above 10 kHz at 4 K is 80 nΦ0 Hz−1∕2 at a bandwidth of 200 MHz. Estimations suggest that one can benefit from parametric gain based on inherent nonlinearity of the Josephson junction and reduce the flux noise to 30 nΦ0Hz–1∕2 at 100 mK, which corresponds to 10.6 μBHz–1∕2 for a magnetic moment located at the center of the pickup loop. [ABSTRACT FROM AUTHOR]

Presents information on a study that reported electroluminescence emission at room temperature from indium-tin-oxide and indium oxide films. Research method; Results and discussion on the study.

We have studied a Superconducting Quantum Interference Device (SQUID) made from a single layer thin film of superconducting silicon. The superconducting layer is obtained by heavily doping a silicon wafer with boron atoms using the gas immersion laser doping technique. The SQUID is composed of two nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at low temperature and low magnetic field. The overall behavior shows very good agreement with numerical simulations based on the Ginzburg-Landau equations. [ABSTRACT FROM AUTHOR]

Nano-Superconducting Quantum Interference Devices (nano-SQUIDs) are usually fabricated from a single layer of either Nb or Al. We describe here a simple method for fabricating suspended nano-bridges in Nb/Al thin-film bilayers. We use these suspended bridges, which act as Josephson weak links, to fabricate nano-SQUIDs which show critical current oscillations at temperatures up to 1.5K and magnetic flux densities up to over 20mT. These nano-SQUIDs exhibit flux modulation depths intermediate between all-Al and all-Nb devices, with some of the desirable characteristics of both. The suspended geometry is attractive for magnetic single nanoparticle measurements. [ABSTRACT FROM AUTHOR]

Scanning SQUID susceptometry images the local magnetization and susceptibility of a sample. By accurately modeling the SQUID signal we can determine physical properties such as the penetration depth and permeability of superconducting samples. We calculate the scanning SQUID susceptometry signal for a superconducting slab of arbitrary thickness with isotropic London penetration depth λ on a nonsuperconducting substrate, where both slab and substrate can have a paramagnetic response that is linear in the applied field. We derive analytical approximations to our general expression in a number of limits. Using our results, we fit experimental susceptibility data as a function of the sample-sensor spacing for three samples: (1) δ-doped SrTiO3, which has a predominantly diamagnetic response, (2) a thin film of LaNiO3, which has a predominantly paramagnetic response, and (3) the two-dimensional electron layer at a SrTiO3/LaAlO3 interface, which exhibits both types of response. These formulas will allow the determination of the concentrations of paramagnetic spins and superconducting carriers from fits to scanning SQUID susceptibility measurements. [ABSTRACT FROM AUTHOR]

We discuss the Meissner response to a known field source of superconductors having inhomogeneities in their penetration depth. We simplify the general problem by assuming that the perturbations of the fields by the penetration depth inhomogeneities are small. We present expressions for inhomogeneities in several geometries, but concentrate for comparison with experiment on planar defects, perpendicular to the sample surfaces, with superfluid densities different from the rest of the samples. These calculations are relevant for magnetic microscopies, such as Scanning Superconducting Quantum Interference Device (SQUID) and Magnetic Force Microscope, which image the local diamagnetic susceptibility of a sample. [ABSTRACT FROM AUTHOR]

We use scanning superconducting quantum interference device (SQUID) microscopy to investigate the behavior of vortices in the presence of twin boundaries in the pnictide superconductor Ba(Fe1-xCox)2As2. We show that the vortices avoid pinning on twin boundaries. Individual vortices move in a preferential way when manipulated with the SQUID: They tend to not cross a twin boundary, but rather to move parallel to it. This behavior can be explained by the observation of enhanced superfluid density on twin boundaries in Ba(Fe1-xCox)2As2. The observed repulsion from twin boundaries may be a mechanism for enhanced critical currents observed in twinned samples in pnictides and other superconductors. [ABSTRACT FROM AUTHOR]

Understanding the nature of the ground state and its low-lying excitations in the copper oxide superconductors is a prerequisite for determining the origin of high-temperature superconductivity. A superconducting order parameter (that is, the energy gap) with a predominantly dx2−y2 symmetry is well-established. However, various deviations from a pure d-wave pair state, such as the possibility of Cooper pairing with broken time-reversal symmetry or an admixed dx2−y2+s pair state, have been theoretically predicted and actively sought in numerous experimental studies. Here, we present an angle-resolved phase-sensitive technique for accurately determining the in-plane pairing symmetry, and demonstrate this technique in optimally doped YBa2Cu3O7−δ. We find that the gap along the b-axis (Cu–O chain) direction is at least 20% larger than that along the a-axis direction, and that any imaginary idxy, is or ip component must be smaller than a few per cent of the dx2−y2 component of the gap. [ABSTRACT FROM AUTHOR]

Understanding the nature of the ground state and its low-lying excitations in the copper oxide superconductors is a prerequisite for determining the origin of high-temperature superconductivity. A superconducting order parameter (that is, the energy gap) with a predominantly dx2−y2 symmetry is well-established. However, various deviations from a pure d-wave pair state, such as the possibility of Cooper pairing with broken time-reversal symmetry or an admixed dx2−y2+s pair state, have been theoretically predicted and actively sought in numerous experimental studies. Here, we present an angle-resolved phase-sensitive technique for accurately determining the in-plane pairing symmetry, and demonstrate this technique in optimally doped YBa2Cu3O7−δ. We find that the gap along the b-axis (Cu–O chain) direction is at least 20% larger than that along the a-axis direction, and that any imaginary idxy, is or ip component must be smaller than a few per cent of the dx2−y2 component of the gap. [ABSTRACT FROM AUTHOR]

We review results on two novel types of grain-boundary Josephson junctions in the high-critical-temperature cuprate superconductors. The quality of YBa2Cu3O7-δ biepitaxial grain-boundary Josephson junctions has been improved using a new growth geometry to the point that “tunnel-like” characteristics are reproducibly obtained. The consequent low barrier transmission probabilities are apparently favorable for isolating intrinsic d-wave induced effects. We also focus on peculiar aspects of spontaneous currents in HTS Josephson junctions, which are unique and reflect the intimate relation between vortex matter and the Josephson effect. Bicrystal grain-boundary Josephson junctions have also been fabricated using artificial superlattice films with as few as six superconducting copper–oxygen planes. Extrinsic and intrinsic d-wave effects in these junctions are discussed within the framework of novel designs for π-circuitry and qubits. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]