high-Tc Dc Superconducting Quantum Interference Research Articles

Towards an electrowetting-based digital microfluidic platform for magnetic immunoassays

We demonstrate ElectroWetting-On-Dielectric (EWOD) transport and SQUID gradiometer detection of magnetic nanoparticles (MNPs) suspended in a 2 microl de-ionized water droplet. This proof-of-concept methodology constitutes the first development step towards a highly sensitive magnetic immunoassay platform with SQUID readout and droplet-based sample handling. Magnetic AC-susceptibility measurements were performed on MNPs with a hydrodynamic diameter of 100 nm using a high-Tc dc Superconducting Quantum Interference Device (SQUID) gradiometer as detector. We observed that the signal amplitude per unit volume is 2.5 times higher for a 2 microl sample droplet compared to a 30 microl sample volume.

Detection of nuclear magnetic resonance in the microtesla range using a high Tc dc-superconducting quantum interference device

We have carried out nuclear magnetic resonance experiments in microtesla range.The free induction signal was recorded using a high Tc dc-superconducting quahtum interference device.The measurement was performed in a home-made magnetic shield room.Resonance spectra of 1H from a sample of 15 ml tap water was obtained in the field range from 7—70 μT，corresponding to resonance frequency of 300—3000 Hz，The signal to noise ratio in a single-shot measurement is around 4，which could be increased to about 40 after 100 times averaging.The effect of residual magnetic field in the shield room， prepolarization time and data acquisition time was investigated.

Analytical results of the Fokker–Planck equation derived for one superconducting nanowirequantum interference device and for DC SQUID: symmetric devices

We consider a symmetric two-junction superconducting quantum interference device,whose junctions are assumed to be overdamped, and consider the sin Fourier seriesfor their current–phase relations. We take into account the effects of thermalfluctuations by forming a two-dimensional Fokker–Planck equation for the distributionfunction. We judge a series expansion of first order with respect to the componentsof the reduced inductance for the distribution function and obtain relations forcurrent–voltage and the circulating current. We consider the measured resistance of thesuperconducting nanowire quantum interference device with mesoscopic leadsthat Hopkins et al reported in Hopkins et al (2005 Science 308 1762) and Pekkeret al (2005 Phys. Rev. B 72 104517), by defining the loop inductance, and byconsidering appropriate relations for the resistance of nanowires. In fact, we extendthe Chesca formulation (Chesca 1998 J. Low Temp. Phys. 112 165) and give aunification formulation for symmetric nanowire two-junction devices, low and highTc DC superconducting quantum interference devices (SQUIDs) in restricted conditions.

High-Tc dc SQUID Cooled by Pulse-Tube Cooler and Corrosion Measurements

We developed an YBCO high-Tc dc superconducting quantum interference device (SQUID) system cooled by a pulse-tube cooler. To stabilize and control the operating temperature of SQUID, a temperature controlling method, using dc SQUID itself as the temperature sensor, was developed. With the temperature controller, the temperature fluctuation could be reduced to about 50 mK and the dc SQUID magnetometer could keep locking for over 8 h. Using this dc SQUID magnetometer, we did some corrosion measurements in shielding. The field produced by the corrosion of aluminum plate with one side immersed in corrosion solution could be successfully detected.

Inductance-dependent characteristics of high-Tc dc-superconducting quantum interference device amplifiers

We have experimentally determined the inductance Lsq, transfer function VΦ, and flux noise SΦ of several dc-superconducting quantum interference devices (SQUIDs) of increasing loop size (without an input flux transformer) in open-loop mode. Our primary aim was to provide reliable inductance data to aid in the design of high temperature superconducting magnetometers. Flux was induced by current injection directly into the SQUID loop. The inductances were compared with theoretical values. Correlations between the inductance data and measured values of VΦ and SΦ were obtained. Guidelines for optimization of magnetometer SQUIDs were established; the importance of achieving large VΦ together with a relatively small Lsq was demonstrated, and an order-of-magnitude reduction in noise was achieved by subjecting one of the SQUIDs to an in-house “ion-beam trimming” process.

Novel excitation coils for non-destructive evaluation of non-magnetic metallic structures by high-Tc dc SQUID

A non-destructive evaluation (NDE) system was set up in our laboratory. A high-Tc dc superconducting quantum interference device (dc SQUID) made from YBa2Cu3O7−δ thin film on a 24° bicrystal SrTiO3 substrate was adopted as the magnetic flux sensor. Novel excitation coils and a balance circuitry were proposed and employed for evaluation of multilayer aluminium structure with artificial slits in an unshielded noisy environment. Our experimental data demonstrate that the NDE system with proper location of two thin excitation coils could make full use of the dynamic range of the SQUID and enhance the spatial resolution of detection.

Shapiro steps observed in a dc superconducting quantum interference device with multiple junctions in each arm

A high-Tc dc superconducting quantum interference device (SQUID) with three Josephson junctions (JJs) in series in each of its arms has been fabricated. Its Shapiro steps were studied using microwave (rf) radiation of 10 GHz and weak magnetic fields. The appearance of giant Shapiro steps and of some of half-integer steps was observed. Separation between the adjacent Shapiro steps could be tuned by rf magnetic fields and small external dc magnetic fields. This phenomenon was analyzed by phase locking the JJs in the SQUID.

Transfer function and noise properties of YBa2Cu3O7−δ direct-current superconducting-quantum-interference-device magnetometers with resistively shunted inductances

We have investigated resistively shunted direct-coupled high-Tc dc superconducting quantum interference device (SQUID) magnetometers with four different inductances (50, 100, 150, and 200 pH). The SQUIDs were based on 200 nm thick YBa2Cu3O7−δ films deposited on bicrystal substrates with a 24° misorientation angle, and the shunt resistors were fabricated by masked ion damage. At T=77 K, good quantitative agreement was observed between the measured maximum voltage modulation depth ΔV and calculated values based on the theoretical predictions by Enpuku et al., whereas the white magnetic flux noise SΦ at 10 kHz of all four devices was found to be a factor of 2.3 higher than predicted. The lowest white magnetic field noise of 153 fT/Hz was obtained for the magnetometer with a SQUID inductance of 100 pH with an outer dimension of the pickup loop of just 2 mm.

Design and realization of an all d-wave dc π-superconducting quantum interference device

The predominantly dx2−y2-pairing symmetry in most high-Tc superconductors provides the opportunity to fabricate Josephson junction circuits in which part of the junctions are biased by a phase difference of the superconducting order parameter of π. We present fabrication and measurements of an all high-Tc dc superconducting quantum interference device (dc SQUID) realized with thin-film technology, of which the Josephson junctions consist of one standard junction and one junction with a π-phase shift. The characteristics of the π-SQUID are compared with the properties of a standard high-Tc SQUID.

Low-field magnetic resonance imaging with a high-Tc dc superconducting quantum interference device

A spectrometer incorporating a high transition temperature dc superconducting quantum interference device (SQUID) is used to obtain nuclear magnetic resonance signals from protons in mineral oil at room temperature in fields up to 3 mT. The spatial separation between the SQUID magnetometer at 77 K and the sample at room temperature is less than 1 mm. At 2 mT, the signal is easily resolved in a single scan. Two-dimensional images of samples consisting of pieces of lucite or glass immersed in mineral oil are obtained at 2 mT.

Current resolution, noise, and inductance measurements on high-T c dc SQUID galvanometers

Single layer autonomous high-Tc dc superconducting quantum interference devices (SQUIDs) have been fabricated and tested. The SQUIDs were designed for application as a galvanometer. The current to be measured is injected directly in a microstrip segment of the SQUID loop. Step-edge as well as bicrystal YBCO Josephson junctions were used. We consider two aspects: (i) optimization of the noise properties with respect to current resolution, and (ii) temperature dependence of the period of voltage-flux relation. The SQUID inductance was calculated numerically taking into account the magnetic field penetration depth λ. The temperature dependence of λ(T) was obtained from experimental results and is found to be in good agreement with λ(T)≊λ(0)[1−(T/TC)2]−1/2.