Dc SQUID Research Articles

Superconductive Circuits and the General-Purpose Electronic Simulator APLAC

The general-purpose circuit simulator analysis program for linear active circuits (APLAC) is not widely known within the superconductor circuit community, regardless of its built-in Josephson junction model and capability of modeling the superconductive phase transition with controlled sources. We review the use of APLAC to model, e.g., noisy dc SQUIDs and transition-edge sensors. Based on an APLAC simulation, we also comment on the preference of voltage bias over current bias in dc SQUIDs in applications where large dynamic range and high bandwidth are simultaneously required.

Room Temperature Magnetic Memory Effect in Nanodiamond/γ-Fe2O3 Composites.

We report a room temperature magnetic memory effect (RT-MME) from magnetic nanodiamond (MND) (ND)/γ-Fe2O3 nanocomposites. The detailed crystal structural analysis of the diluted MND was performed by synchrotron radiation X-ray diffraction, revealing the composite nature of MND having 99 and 1% weight fraction ND and γ-Fe2O3 phases, respectively. The magnetic measurements carried out using a DC SQUID magnetometer show the non-interacting superparamagnetic nature of γ-Fe2O3 nanoparticles in MND have a wide distribution in the blocking temperature. Using different temperature, field, and time relaxation protocols, the memory phenomenon in the DC magnetization has been observed at room temperature (RT). These findings suggest that the dynamics of MND are governed by a wide distribution of particle relaxation times, which arise from the distribution of γ-Fe2O3 nanoparticle size. The observed RT ferromagnetism coupled with MME in MND will find potential applications in ND-based spintronics.

Holographic DC SQUID in the presence of dark matter

The gauge-gravity duality has been applied to examine the properties of holographic superconducting quantum device (SQUID), composed of two S-N-S Josephson junctions, influenced by dark sector modelled by the additional U(1)-gauge field coupled to the ordinary Maxwell one. The dark matter sector is known to affect the properties of superconductors and is expected to enter the current-phase relation. The kinetic mixing between two gauge fields provides a mechanism allowing for the conceivable observation of the effect. We find small but visible effect of the dark matter particle traversing the device, which shows up as a change of its maximal current.

Разработка джозефсоновского параметрического усилителя бегущей волны нa основе алюминиевых СИС-переходов

We designed, fabricated, and tested several prototypes of a Josephson Travelling Wave Parametric Amplifier (JTWPA) with aluminum SIS junctions integrated in series array of dc SQUIDs in the central line of coplanar waveguide. Three types of fabrication recipes were tested: two with shadow evaporation and one with magnetron sputtering and direct e-beam lithography. IV curves of SQUIDs were measured at bath temperature of 0.3 K. We developed a cryogenic setup for meas-urements of spectral characteristics of JTWPA comprising cold HEMT amplifier with circulator, cold attenuators and filters in signal and pump coaxial lines. Resonant characteristic of coplanar quarter-wave resonator with directional coupler intended for short JTWPA was measured.

Fe-C nanoparticles obtained from thermal decomposition employing sugars as reducing agents

The aim of the work is to present a comparative analysis (structural and magnetic) of Fe-C nanocomposites obtained by the thermal decomposition of sugars (fructose, glucose and sucrose) employing FeCl3 as Fe3+ precursor. The thermal decomposition was followed through Thermogravimetry (TGA) and Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction, High Resolution Transmission Electron Microscopy (HRTEM) and Raman spectroscopy. The results indicate the reduction of Fe3+ under the performed thermal treatments and the achievement at high annealing temperatures of Fe-C nanostructures (coexistence of α-Fe and Fe3C nanoparticles surrounded by a carbon matrix). The magnetic characterization performed by dc SQUID magnetometry, shows an antiferromagnetic response in the initial stages of the decomposition process, and a ferromagnetic behavior linked to the Fe-based nanoparticles. The magnetic induction heating was analyzed through the ac hysteresis loops. Moderate Specific Absorption Rate (SAR) is obtained in Fe-C nanoparticles (~ 70 W/gFe), ascribed to the large nanoparticle size. The combination of porous carbon structure and ferromagnetic response of the Fe-C nanoparticles (i.e. local temperature increase under ac magnetic field) enlarge the emerging applications of these carbonaceous nanocomposites.

Analysis of LC-Resonance in DC SQUID Using Dynamic System Model

Direct current superconducting quantum interference device (dc SQUID) can be regarded as a hybrid system with two nonlinear Josephson currents driving a linear network consists of conventional resistors (R), inductors (L), and capacitors (C). There must be LC resonances inside the SQUID loop with influences on its static current-voltage characteristics. To study the working principle of the LC resonance, we build an equivalent dynamic system model transformed directly from the circuit equations of dc SQUID. With dynamic system analyses in both dc and alternating current (ac) domains, we derive the analytical expressions of the resonance point with only the RLC circuit parameters. The analytical derivation proves that the LC resonance inside a symmetrical dc SQUID with resonance frequency ω = 1/√LC results in the flux modulation suppression with I-V curves concentrated on one resonance point. Based on those mathematical expressions, the resonance point is easily indentified from the measured I-V curves, and can be utilized for practical SQUID parameters characterization.

Critical current of dc SQUID on Josephson junctions with unconventional current-phase relation

Here we present calculations of the critical current of dc SQUID based on Josephson junction with un-conventional current-phase relation. We analyzed two cases of current-phase relation of junction: with anhar-monic and Majorana term. It is shown that the changing of the critical current in the case of the small geo-metrical inductance of dc SQUID based on Josephson junctions with unconventional current-phase relation is determined by the amplitude of the second term in current-phase relation, the geometrical inductance of dc SQUID and external magnetic field. In the case of the high inductance of dc SQUID unconventional terms can be ignored.

Simulation and visualization of the interference phenomena inside DC SQUID with interferometric circuit model

Flux modulated static current-voltage characteristics are the basis of DC SQUID being the flux-to-voltage convertor utilized in high-performance magnetic field measurement systems. Those static behaviors are the results of the internal quantum interference between two Josephson junctions. However, the interferometric working principle and the interference phenomena are difficult to be intuitively visualized, either through simulation with conventional models, or through the in-situ measurement inside DC SQUID. Therefore, we redraw the equivalent circuit of DC SQUID in form of the microwave interferometer, and transform it into a concise dynamic system model to study the interferometric mechanism. The double-slit like interference phenomena inside the DC SQUID are visualized through simulations of the AC oscillation current and voltage along the SQUID washer. The concept that DC SQUID is a microwave integrated circuit working as the microwave interferometer rather than a static nonlinear transducer is demonstrated and emphasized. Those concepts help users and designers improve their understandings of quantum interference mechanism of DC SQUID for both circuit design and the practical application system development.

A SQUID-Based Picovoltmeter for Quantum Resistors

We present a sensitive voltage amplifier suited for measurements of source impedances in the k $$\Omega$$ range at dilution refrigerator temperatures. The circuit is based on a commercial dc SQUID, an impedance matching transformer, and it works on the principle of negative feedback. At 10 mK, the amplifier contribution to the noise is only 17 $$\text{pV/}\sqrt{\text{ Hz }}$$ , which is negligible in comparison with the fluctuations of the thermal voltage of a 3.25 k $$\Omega$$ metallic source resistor. Various circuit parameters of the amplifier are discussed.

Small capacitance self-shunted MoRe–Si(W)–MoRe junctions for SQUIDs applications

MoRe–Si(W)–MoRe planar Josephson junctions with a hybrid barrier layer made of amorphous silicon doped with tungsten at relatively high tungsten concentrations (~ 11%) are experimentally studied. Small intrinsic (natural) capacitance and shunting by tungsten nanoclusters give an advantage to MoRe–Si(W)–MoRe junctions against traditional superconductor–insulator–superconductor (SIS) planar junctions as candidates for innovative superconducting electronics. It is shown that the use of such junctions with a Si(W) barrier layer thickness of 15–30 nm can substantially enhance the sensitivity of both RF and DC SQUIDs.

NanoSQUIDs from YBa2Cu3O7/SrTiO3 superlattices with bicrystal grain boundary Josephson junctions.

We report on the fabrication and characterization of nanopatterned dc SQUIDs with grain boundary Josephson junctions based on heteroepitaxially grown YBa2Cu3O7 (YBCO)/SiTrO3 (STO) superlattices on STO bicrystal substrates. Nanopatterning is performed by Ga focused-ion-beam milling. The electric transport properties and thermal white flux noise of superlattice nanoSQUIDs are comparable to single layer YBCO devices on STO bicrystals. However, we find that the superlattice nanoSQUIDs have more than an order of magnitude smaller low-frequency excess flux noise, with root-mean-square spectral density at 1 Hz (Φ0 is the magnetic flux quantum). We attribute this improvement to an improved microstructure at the grain boundaries forming the Josephson junctions in our YBCO nanoSQUDs.

Characterization of TDEM System With SQUID and Fluxgate Magnetometers for Geophysical Applications

This article describes the characterization of the SQUID-based time domain electromagnetic (TDEM) system for use in geophysical applications. This system has been characterized near the laboratory where the background noise, especially the cultural noise, is relatively low. A transmitter loop in the form of a square (2 × 2 m) with the excitation current of 0.212 A in the form of modified square pulses with a frequency of 2.5 Hz has been used to induce eddy currents in a nearby conducting target. A three-axes low Tc dc SQUID magnetometer and its associated fast readout electronics have been used to record the transient response of the target. Meanwhile, as part of this developmental work and to get the field experience, the TDEM measurements have been performed in the field with transmitter loop size of 100 × 100 m and fluxgate magnetometer as a receiver. Here, we observed that the decay of the secondary magnetic field has always unexpectedly reached a negative value even at the earlier time windows. Subsequently, the TDEM experiments with fluxgate as the receiver have been repeated with the same configuration as done in the past with SQUID, and the performance of the magnetometers, such as fluxgate and SQUID, have been compared. The experimental results were analyzed in detail and show that the fluxgate magnetometer behaves as the combination of magnetic field sensor and induction coil at earlier decay times, and magnetic field sensor only at later decay times.

Flux-Driven Josephson Traveling-Wave Parametric Amplifier

We have developed a concept for a traveling-wave parametric amplifier driven by a magnetic flux wave. The circuit consists of a serial array of symmetric dc SQUIDs coupled inductively to a separate superconducting LC transmission line carrying the pump microwave; thereby the signal and pump are applied to different ports. The proposed three-wave-mixing amplifier includes, firstly, an adjustable phase velocity of the signal (idler) wave and hence good phase matching yielding large gain in a wide frequency range and, secondly, overcoming of the pump depletion problem. The experimental parameters and characteristics of this amplifier have been evaluated and show promise for applications in quantum-information single-photon circuits.

Quantum interference effects in 1D parallel high-Tc SQUID arrays with finite inductance

The quantum interference effects of one-dimensional (1D) parallel arrays of high-temperature superconducting (HTS) SQUIDs were investigated experimentally and theoretically via the voltage–magnetic field responses for 4–81 Josephson junctions. The sensitivity of the arrays generally decreased as the number of junctions (and SQUIDs) in parallel increased, contrary to the predictions of models in the low (zero) inductance limit. A full theoretical description was developed to describe 1D parallel HTS SQUID arrays with finite inductances in an applied magnetic field, by extending the model for a single DC SQUID to multiple loops in parallel and including the flux generated by currents circulating through all loops in the array. Calculations were extended from SQUID arrays with equal loop areas to arrays with a distribution of loop areas, otherwise known as superconducting quantum interference filters. The model uses parameters relevant to HTS arrays, including typical variations (up to 30%) in HTS Josephson junction parameters, such as critical current and normal resistance. The effect of the location of the current biasing leads was also explored through the calculations. This model shows good agreement with experimentally measured 1D arrays of different lengths and highlights the importance of the geometry of the current biasing leads to the arrays when optimizing the array response.

Magnetic Properties of Poly(trimethylene terephthalate‐block‐Poly(tetramethylene oxide) Copolymer Nanocomposites Reinforced by Graphene Oxide–Fe3O4 Hybrid Nanoparticles

Thermoplastic elastomeric nanocomposites based on poly(trimethylene terephthalate‐block‐poly(tetramethylene oxide) copolymer (PTT‐PTMO) and graphene oxide (GO)–Fe3O4 nanoparticles hybrid are prepared by in situ polymerization. Superparamagnetic GO–Fe3O4 hybrid nanoparticles before introducing to elastomeric matrix are characterized by X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The effect of loading (0.3 and 0.5 wt%) of GO–Fe3O4 nanoparticle hybrid on the phase structure, tensile, and magnetic properties of synthesized nanocomposites is investigated. The phase structure of nanocomposites is evaluated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Dispersion of GO–Fe3O4 nanoparticles in elastomeric matrix is evaluated by transmission electron microscopy (TEM). Magnetic properties of GO–Fe3O4 nanoparticle hybrid and nanocomposites with their content are characterized using two different techniques: direct current superconducting quantum interference device (dc SQUID) magnetization measurements as a function of temperature (from 2 to 300 K) and external magnetic field and ferromagnetic resonance (FMR) at microwave frequency.

Two-terminal wide range SQUID amplifier with hysteretic quasi linear transfer characteristics

To implement wide range measurement using direct current Superconducting Quantum Interference Device (dc SQUID), we presented a simple two-terminal SQUID amplifier consists of a shunt resistor and a conventional SQUID in series with feedback coil. Only two terminals are led out with coaxial cable for high speed and low heat loss. Periodically repeated quasi linear flux-to-voltage transfer characteristics are achieved by internal flux feedback. Wide range flux input is modulated by the SQUID amplifier into voltage signal with rapid transient edges. The reconstructed output is the synthesis of measured voltage and counts of flux-quanta counting. Working principles of linearized SQUID amplifier were simulated and experimentally verified. Wide range measurement with error within ±0.1Φ0 was demonstrated in the experiment.

Performance of DC SQUID Second-Order Axial Gradiometer Response to Radio Frequency Interference

A low-Tc dc SQUID placed in a superconducting and magnetic shield is insensitive to magnetic interference, but not completely immune to the effects of radio frequency interference (RFI). Here, we investigated the effect of two orthogonal RF fields on the second-order axial gradiometer's transfer characteristics and noise characteristics. RF field induced phase shift of the V – $\Phi$ curve. The modulated spikes of RF field on the V – $\Phi$ curve and noise spectrum became significant with the RF field increasing. The white noise of the system increased to 12.5 $fT/\sqrt{\text{Hz}}$ with +10 dB axial RF field, nearly one and a half times of 8.5 $fT/\sqrt{\text{Hz}}$ without RFI. The working point jumping occurred under the radial RF field of +5 and +10 dB, and the white noise increased to 17.2 and 165.8 $fT\sqrt{\text{Hz}}$ , respectively. The reason of work point drift related to the magnetic flux coupling between the SQUID and pickup coil needs further studies.

A linear magnetic flux-to-voltage transfer function of a differential DC SQUID

A superconducting quantum interference device with differential output or ‘DSQUID’ was previously proposed for operation in the presence of large common-mode signals. The DSQUID is the differential connection of two identical SQUIDs. Here we show that besides suppression of electromagnetic interference this device provides effective linearization of the DC SQUID voltage response. In the frame of the resistive shunted junction model with zero capacitance, we demonstrate that spur-free dynamic range of the DSQUID magnetic flux-to-voltage transfer function is higher than 100 dB while the total harmonic distortion of a signal is less than 10−3% with a peak-to-peak amplitude of a signal being a quarter of half flux quantum, 2Φa = Φ0/8. Analysis of the DSQUID voltage response stability to a variation of circuit parameters shows that DSQUID implementation allows for highly linear magnetic flux-to-voltage transformation at the cost of a high identity of Josephson junctions and high-precision current supply.

A new limit of the 129Xenon Electric Dipole Moment

We report on the first preliminary result of our 129Xe EDM measurement performed by the MIXed collaboration. The aim of this report is to demonstrate the feasibility of a new method to set limits on nuclear EDMs by investigating the EDM of the diamagnetic 129Xe atoms. In our setup, hyperpolarized 3He serves as a comagnetometer needed to suppress magnetic field fluctuations. The free induction decay of the two polarized spin species is directly measured by low noise DC SQUIDs, and the weighted phase difference extracted from these measurements is used to determine a preliminary upper limit on the 129Xe EDM.

Advanced HTS DC SQUIDs with Step-Edge Josephson Junctions for Geophysical Applications

For ground-based electromagnetic methods in geophysics dc superconducting quantum interference devices based on high-temperature superconductors are well suited as magnetic field sensors. Therefore, we introduce in this paper an advanced fabrication technology for high-temperature superconducting dc SQUIDs based on step-edge Josephson junctions. The dc SQUIDs are prepared on structured magnesium-oxide substrates. A trilayer of YBa 2 Cu 3 O 7-x /SrTiO 3 /YBa 2 Cu 3 O 7-x is deposited by pulsed laser deposition and structured with ion beam etching. The galvanometer-type design consists of four different dc SQUIDs directly coupled to a pickup loop. They exhibit large I c R n products and a voltage swing of more than 30 μV. The magnetic field noise amounts to about 20 fT/Hz 1/2 and 35 fT/Hz 1/2 for the white noise region as well as 25 fT/Hz 1/2 and 100 fT/Hz 1/2 at 100 Hz for ac-bias and dc-bias SQUID electronics, respectively. The advanced fabrication process thus enables to produce HTS dc SQUIDs intended for the use in geophysical applications with high throughput.