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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.

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.

A magnetic domain boundary on the surface of a three-dimensional topological insulator is predicted to host a chiral edge state, but direct demonstration is challenging.We used a scanning superconducting quantum interference device to show that current in a magnetized topological insulator heterostructure (EuS/Bi2Se3)f lows at the edge when the Fermi level is gate-tuned to the surface band gap.We further induced micrometer-scale magnetic structures on the heterostructure and detected a chiral edge current at the magnetic domain boundary. The chirality of the current was determined bymagnetization of the surrounding domain, and its magnitude by the local chemical potential rather than the applied current. Such magnetic structures provide a platformfor detecting topologicalmagnetoelectric effects andmay enable progress in quantum information processing and spintronics. [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]

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]

Focuses on the measurement of symmetry of superconducting order parameter. Tests for d-wave symmetry in YBa(...)Cu(...)O(...); Samples with varying parameters; Calibration of intensity of scanning superconducting quantum interference device.

A scanning tunneling microscope capable of operating at low temperatures, T=400 mK, and in high magnetic fields, B=8 T, is described. Accompanying electronics, under the control of an IBM PC/AT, provide routine spatially resolved spectroscopy, allowing characterization of properties such as superconducting energy gaps and local density of states on the surface. Data are presented to illustrate the usefulness of spatially resolved spectroscopy at low temperatures and in high magnetic fields. [ABSTRACT FROM AUTHOR]

We employed a scanning Hall probe microscope to detect the hopping of individual vortices between pinning sites along grain boundaries in YBa2Cu3O6+δ thin films in the presence of an applied current. Detecting the motion of individual vortices allowed us to probe the current-voltage (I-V) characteristics of the grain boundary with voltage sensitivity below a femtovolt. We find a very sharp onset of dissipation with V∝In with an unprecedented high exponent of n≈290 that shows essentially no dependence on temperature or grain boundary angle. Our data have no straightforward explanation within the existing grain boundary transport models. [ABSTRACT FROM AUTHOR]

We have simultaneously measured the surface topography and the tunneling current-voltage (I-V) characteristics of thin films of NbN as a function of lateral position using a low-temperature scanning tunneling microscope. We have imaged the superconducting energy gap by fitting the I-V’s with an energy gap for each spatial position. Such images showed significant variation of the gap, including areas with reduced gap when a magnetic field (up to 6 T) was applied. The features in the gap image were often correlated with features in the surface topographic images. [ABSTRACT FROM AUTHOR]

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]

It is of interest to determine the exit angle of a vortex from a superconductor surface, since this affects the intervortex interactions and their consequences. Two ways to determine this angle are to image the vortex magnetic fields above the surface, or the vortex core shape at the surface. In this work we evaluate the field h(x,y,z) above a flat superconducting surface x,y and the currents J(x,y) at that surface for a straight vortex tilted relative to the normal to the surface, for both the isotropic and anisotropic cases. In principle, these results can be used to determine the vortex exit tilt angle from analyses of magnetic field imaging or density of states data. [ABSTRACT FROM AUTHOR]

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.

A correction to the article "Observation of chiral currents at the magnetic domain boundary of a topological insulator," by Y. H. Wang and colleagues in the 2015 issue.

We describe aluminum-niobium-tungsten trilayer Nano-Superconducting Quantum Interference Devices (NanoSQUIDs) that can be read out continuously down, in temperature, to at least 230 mK. They show voltage oscillations up to at least 20 mT in field. A voltage modulation of 500 μV, voltage sensitivity of 2 mV/[uppercase_phi_synonym]0, and white noise floor better than [formula] have been obtained. Flux noise places them between conventional low impedance SQUIDs and standard nanoSQUIDs. High sensitivity and ease of implementation make this new kind of nanoSQUID attractive for magnetic detection schemes on the nanoscale and low temperature scanning SQUID microscopy. [ABSTRACT FROM AUTHOR]

A correction to the article "Angle-resolved phase-sensitive determination of the in-plane gap symmetry in YBa2Cu3O7δ" that was published in the February 5, 2006 issue is presented.

We have measured the subgap current at 0.8 K in several hysteretic 1.5×1.6 and 2.6×2.6 μm2 Nb/AlOx/Nb tunnel junctions. In zero magnetic field, the critical current Ic∼8 μA and the subgap resistance R∼0.3 MΩ. When we apply a magnetic field, Ic can be as low as 1 nA, and R is larger than 1 GΩ. This means that in a superconducting qubit made using Nb tunnel junctions, the decoherence rate from the quasiparticle conductance may be as low as 1/(100 μs). [ABSTRACT FROM AUTHOR]

A method for altering the local direction and angular dispersion of anisotropy in soft magnetic films using energetic ion irradiation is demonstrated. NiFe films 50 Å thick were irradiated with 200 keV Ar[sup +] ions to doses between 10[sup 13] and 10[sup 16] ions/cm², while a saturating magnetic field was applied to the samples. This annealing field defined the new anisotropy direction of the irradiated areas, and the irradiation process also led to changes in the angular dispersion of anisotropy orientation, as measured by angle-dependent remanence of magnetization. By appropriate masking of films, this technique has been used to pattern samples with small "anisotropy domains". [ABSTRACT FROM AUTHOR]

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]

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]

We study how coexisting states of superconductivity and magnetism interact with each other by local measurements of the magnetic fields, with micron scale spatial resolution, above a single crystal of the ferromagnetic superconductor UCoGe using scanning superconducting quantum interference device microscopy. Our measurements show that the spontaneous ferromagnetic transition at Tc = 2.5 K is characterized by Ising-like magnetization along the easy axis (c direction), with domain sizes of the order of 10 pm, magnetization amplitudes of 45 G, and are consistent with estimates of domain-wall widths of several angstroms. The measured magnetization amplitudes are in agreement with bulk magnetization measurements, implying that domain reconstruction at the sample surface is negligible. In the superconducting state, which coexists with ferromagnetism below Tsc = 0.67 K, both diamagnetic screening and Meissner expulsion of flux, but no shrinkage of the ferromagnetic domains, are detected. Although we could not resolve individual vortices, our measurements provide evidence for the existence of the spontaneous vortex state in UCoGe. [ABSTRACT FROM AUTHOR]

Expressions for the thermal noise from a collection of exchange-biased magnetic nanoparticles are derived and used to analyze the magnetic noise from thin films of partially oxidized nanoparticles. Functionalized Co nanoparticles with diameters between 3 and 6 nm were oxygenated in solution and then deposited on oxidized silicon substrates, self-assembling into arrays of magnetic nanoparticles during solvent evaporation. Magnetization measurements exhibited the development of exchange bias with oxygenation as evidenced by an increasing exchange field and coercivity. Noise measurements of the exchange-biased nanoparticles using a microsuperconducting quantum interference device sensor are shown to be consistent with theoretical expectations and are used to extract the magnetic energy distributions of the Co/CoO nanoparticles. [ABSTRACT FROM AUTHOR]

The physics of the superconducting state in two-dimensional (2D) electron systems is relevant to understanding the high-transition-temperature copper oxide superconductors and for the development of future superconductors based on interface electron systems. But it is not yet understood how fundamental superconducting parameters, such as the spectral density of states, change when these superconducting electron systems are depleted of charge carriers. Here we use tunnel spectroscopy with planar junctions to measure the behaviour of the electronic spectral density of states as a function of carrier density, clarifying this issue experimentally. We chose the conducting LaAlO3-SrTiO3 interface as the 2D superconductor, because this electron system can be tuned continuously with an electric gate field. We observed an energy gap of the order of 40 microelectronvolts in the density of states, whose shape is well described by the Bardeen-Cooper-Schrieffer superconducting gap function. In contrast to the dome-shaped dependence of the critical temperature, the gap increases with charge carrier depletion in both the underdoped region and the overdoped region. These results are analogous to the pseudogap behaviour of the high-transition-temperature copper oxide superconductors and imply that the smooth continuation of the superconducting gap into pseudogap-like behaviour could be a general property of 2D superconductivity. [ABSTRACT FROM AUTHOR]

Monodisperse magnetic nanoparticles (NPs) could enable the ultra-sensitive magnetic detection of biological analytes. However, rendering these particles biocompatible has remained a challenge. We report the bio-functionalization and detection of 12-nm manganese ferrite NPs. We have achieved the site-specific binding of biotin-functionalized NPs onto avidin-patterned silicon oxide substrates and DNA-functionalized NPs onto complementary DNA-patterned silicon oxide substrates. Utilizing scanning SQUID microscopy, we show that these substrate-bound NPs retain their magnetic properties. Finally, we demonstrate a novel method of detecting either protein binding or DNA hybridization at room temperature using the NPs and a magnetic tunnel-junction-based biosensor situated in orthogonal magnetic fields. [ABSTRACT FROM AUTHOR]