Applied Superconductivity最新文献

Metal(Al,Ag,Au)/ferroelectric (Pb(Zr_0.52Ti_0.48)O₃ [PZT])/high-T_c superconductor ((Y_1-x Pr_x)Ba₂Cu₃O_7-y [YPBCO]) structures have been fabricated by ArF excimer laser deposition. Ferroelectric properties of c-axis oriented epitaxial PZT films on YBa₂Cu₃O_7-y[YBCO]//SrTiO₃3(100) have been studied as a function of temperature in the range of 20–290 K. Samples with three kinds of metal electrode show almost similar ferroelectric properties at 290 K. The remanent polarization and coercive field are about 25 μC/cm² and 146 kV/cm, respectively. At low temperature, on the contrary, the ferroelectric properties of heterostructures were strongly influenced by the choice of the electrode metal. It seems that these properties are severely affected by interface states of metal PZT. The Au electrode gives rise to the best ferroelectric property of PZT films. We also investigated the ferroelectric field effect in the heterostructures of Au/ PZT/(Y_0.6Pr_0.4)Ba₂Cu₃O_7-y. A large modulation (as much as ∼40%) and memory effects are observed in the low frequency source–drain current response to a pulsed voltage.

The unshunted (un) SQUID (superconducting quantum interference device) is a novel device with a frequency-dependent damping on the Josephson junctions. The un SQUID circuit contains four adjustable parameters, including equivalents of the β_c and β_l in dc SQUIDs. We have studied numerically the effect of the parameters to the un SQUID characteristics. To solve the Langevin equations, explicit Euler integration is used. We have also mapped the device noise as a function of the parameters. The energy resolution of the un SQUID appears to be better than that of the dc SQUID.

Y₁Ba₂Cu₃O_x films were grown on MgO(100) substrates by liquid phase epitaxy and their structural and electrical properties were examined. From transmission electron microscopy (TEM) plan-view images, it was found that the films consisted of large grains whose misorientation angles were less than 1°. Although d.c. critical current density values decreased with increasing film thickness, even a 7 μm-thick film showed the value of 9×10⁵ A/cm² at 77 K. An rf first penetration field of the film is estimated to be 30 Oe at 10.8 GHz and 77 K, by using a microstrip line resonator with a resonant frequency of 10.8 GHz. The third-order intercept point of the resonator is at an input power of +43 dBm and output power of +30 dBm at 77 K. These results suggest that LPE grown Y₁Ba₂Cu₃O_x films have superior d.c. and rf electrical properties.

Random telegraph voltage noise signals characterized by strongly nonlinear and nonmonotonic dependence of the telegraph amplitude on current flow has been observed in good quality epitaxial BiSrCaCuO thin film strips biased with d.c. current flow and immersed in an external magnetic field. The shape of the amplitude dependence on current flow closely resembled that observed previously in granular films, where intergranular Josephson junctions were involved in noise generation. The dependence of noise amplitude on bias current and magnetic field in epitaxial films is discussed in the context of the possible Josephson flux-to-voltage conversion mechanism.

We investigated the main dependencies of the gradient resolution of planar galvanometer superconducting quantum interference device (SQUID) gradiometers made of YBa₂Cu₃O_7-x (YBCO). We focussed especially on the influence of antenna layout and the parameters of the galvanometer SQUID such as effective and parasitic areas on the performance of the gradiometer and the behavior in an unshielded environment. The efficiency (that is, the quotient of effective area to inductance) of different geometries of antennas will be compared. Some aspects of the layout of the galvanometer SQUIDs are discussed in terms of parasitic area and best current resolution. Special problems due to the use of bicrystal Josephson junctions in gradiometers for operation in highly disturbed environment are shown. Step-edge Josephson junctions can offer alternative concepts. Reached gradient sensitivity values in the white noise region are 0.46 pT/(cm/$\text{H}$z) in the case of bicrystal junctions and 0.69 pT/(cm/$\text{H}$z) for step-edge junctions.

We present some numerical simulation results for a non-latching Josephson gate which is referred as a coupled-superconducting quantum interference device (SQUID) (C-SQUID) gate. TheC-SQUID gate can perform several logic functions by tuning the bias current to the single-junction-SQUID input-stage. The encoder and the decoder composed of C-SQUID BUFFER and NOR gates are successfully simulated. A modified C-SQUID gate which utilizes kinetic inductance of Josephson junctions is also presented.

Two-dimensional arrays of shunted Nb/AlOx/Nb Josephson junctions have been investigated. Shapiro steps in the current–voltage (I–V) curve of an on-chip detector junction can be used to sense mutual phase locking of the array junctions. By scanning the array with a low-power electron beam, the phase locked junctions remain locked, whereas the unlocked junctions generate a beam-induced additional voltage drop along the array. In regions of the array’s bias current where pronounced Shapiro steps occur in the detector’s I–V curve, practically no array junction generates a beam-induced voltage signal, thus indicating complete mutual locking. For other bias currents of the array with less than maximum detected power, some of the junctions generate beam-induced signals, and can be identified as being non-locked. Our investigations allow a detailed and spatially resolved analysis of mutual phase locking in arrays of Josephson junctions. Moreover, the results obtained with autonomous arrays are compared to experiments performed with injection locked arrays.

A resistive d.c. SQUID (superconducting quantum interference device), d.c. RSQUID for short, is a superconducting loop that contains two shunted Josephson junctions and a resistor. Our d.c. RSQUIDs are intended for noise thermometry below 4.2 K. They are fully integrated thin film devices fabricated in standard Nb technology. The resistor is made from an evaporated silver layer. It is specially designed in order to suppress the proximity effect, and thus the resistor remains normally conductive down to mK temperatures.

For read-out, modified d.c. SQUID electronics are used. It is directly coupled to the d.c. RSQUID and represents a preamplifier with a voltage noise of 0.8 nV/Hz^1/2, a gain of 4000, and a bandwidth of 4 MHz.

Due to this large bandwidth, the d.c. RSQUID can be operated at a high frequency enabling a short averaging time for the temperature measurement. At a frequency of 2 MHz and a temperature of 4.2 K we measured the temperature with a statistical uncertainty of 0.8% for 500 s averaging time.

We report recent progress on an all-electronic, on-chip, 100 mK refrigerator. This refrigerator utilizes the unique thermal transport properties of a normal-insulator-superconductor (NIS) tunnel junction to preferentially remove electrons whose energy is higher than the Fermi energy from the normal electrode, and thus, to lower the temperature of electrons in the normal electrode. We present the first measurements demonstrating electron cooling in a device having a substantially larger area (∼10⁴ μm²) than typical submicron-scale devices demonstrated previously. The performance of this refrigerator is analyzed by a simple thermal model that includes energy transport through the junction, thermal loading from the environment, recombination of quasiparticles in the superconductor electrode, and non-ideal junction characteristics.

A Josephson 256 word×16 bit RAM that includes a power circuit has been designed to enable high-frequency clock operation. This RAM consists of a 4×4 matrix array of 256 RAM blocks, impedance matching lines, and input signal amplifiers. A power-supply circuit, composed of a transformer and a Josephson regulator, is included in each 256 RAM block. Fail bit maps for the 256 RAM block were measured, and perfect operation with a 100% bit yield was obtained. The 256 RAM block functioned properly at a high clock frequency of 1 GHz with less than 3 mW of power dissipation from an external power source.