Microwave-induced Dc Voltages Research Articles

Modulated Structural Characteristics and Microwave Properties of Spray Pyrolyzed Superconducting BCSCO Films

Low-cost–based high-Tc superconducting thin film of Bismuth Strontium Calcium Cuprate on yittriya stabilized zirconia (YSZ) using spray pyrolysis deposition technique from nitrate precursors followed by rapid annealing at temperatures between 830 and 840°C in air and in O2 is described. The films are highly oriented with the c-axis parallel to the plane of the substrate. Some satellite reflections that occur due to the modulation along the crystal lattice (parallel to c-axis) are observed. The prominent X-ray diffraction lines can be fitted to a tetragonal structure. A number of satellite X-ray reflections lines are observed which suggest the existence of modulation. These lines have been fitted in a superspace group \(({\text{N}}\mathop {{\text{III}}}\limits^{{\text{Bb}}\underline {\text{m}} {\text{b}}} )\) with a = 3.832 A and c = 48.826 A indicating the existence of superposed modulated structure. Substrates (Al2O3, LiNbO3, Si3N4, Si) other than YSZ could not produce superconducting films due to the diffusion of metal ions in the film causing poisoning effect in superconducting properties. Resistivity measurements indicate superconducting onset at 92 K and zero resistance at 77 K. Microwave induced dc voltage (μV) measurements as a function of microwave power (mW) were carried out at different temperatures down to 65 K for different annealing temperatures. It is noted that the slope of the line (μV vs. mW) are dependent on ramping of the processing temperatures. The decrease of slope suggested that weak-links between the superconducting grains are decreased as the ramping of the processing temperature is decreased keeping the ramping time constant. The interactions between film and the substrate are qualitatively discussed.

Gamma Ray Irradiation Effects on Electrical Transport and Microwave Properties of BISCO Superconducting Films

High-Tc Superconducting films of Bi–Sr–Ca–Cu–O (2:2:1:2) have been synthesized by spray pyrolysis of nitrate precursors onto yttria stabilized zirconia (YSZ). γ-ray irradiation of the sample, was carried out using a 60Co source of 103 Ci strength for several hundreds of hours; the dose received by the samples was 80 K rad/hr. Superconducting properties such as critical transition temperature (Tc), resistivity (R), critical current density (Jtc). Voltage-time relaxation (Vt) and microwave induced dc voltage were investigated as a function of temperature down to 77 K after γ-ray irradiation. γ-ray irradiation was found to have practically no effect on its structural modification and on the critical transition temperature. However, transport critical current density (Jtc) increased. The increase of pinning energies with irradiation suggests that these changes in properties are dominated by radiation-induced randomly distributed mobile oxygen defects in the films. An appreciable decrease in the microwave-induced dc voltage at 77 K was also observed after irradiation which suggests that the mobile defects are clustered at the major defect region and reduce the total number of weak links. These results suggests that oxygen defects induced by γ-ray irradiation of BISCO films act as important and major pinning centers which is responsible for the enhancement of Jtc and reduction of microwave induced dc voltage.

Microwave-induced dc voltages in a YBa2Cu3O7- delta single crystal.

Microwave-induced dc voltages in a YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} single crystal have been observed along its {ital c} axis with or without a dc bias current by utilizing standing waves near the end of an X-band (8{endash}12 GHz) waveguide. With a dc bias current present, the induced voltages arise from both bolometric and nonbolometric effects; however, the characteristics of the induced voltages versus bias currents due to these two effects are distinctively different. In the bolometric effect, the induced voltages are simply due to a resistive change caused by microwave heating whereas the induced voltages from the nonbolometric effect are due to the Josephson vortex flow generated by the microwave {ital H} field below the superconducting transition temperature. Without a dc bias current, the induced voltages are attributed to the inverse ac Josephson effect which requires the presence of both the microwave {ital E} and {ital H} fields. {copyright} {ital 1996 The American Physical Society.}

Observation of microwave induced dc voltages in a YBa 2Cu 3O 7−δ single crystal

Microwave induced dc voltages in a YBa 2Cu 3O 7−δ single crystal have been observed along its c-axis with or without a dc bias current by utilizing standing waves near the end of an X-band (8–12 GHz) waveguide. With a dc bias current, the effect is larger when the single crystal is coupled to the maximum of the microwave H-field, suggesting that the induced dc voltages are due to vortes flow. Without a dc bias current, the induced voltages resemble the inverse ac Josephson effect and require the presence of both the E- and H-fields of the microwave. The temperature and the bias current dependences of the induced voltages both show several peak structures indicating the existence of multiple Josephson junctions inside a single crystal sample.

Low-temperature magnetic and microwave studies of Gd0.95Ba2Cu3.05O7??: Agx composites

Gd[sub 0.95]Ba[sub 2]Cu[sub 3.05]O[sub 7-[delta]]: Ag[sub x] (x = 0.0, 0.02, 0.04, 0.06) ceramic superconducting samples were prepared by a co-precipation technique using organic carbonates in the presence of stable polymers. The room-temperature normal-state resistivity decreases with Ag addition. However, T[sub c] and crystallographic parameters were unaffected. Low-temperature (4.2 K) magnetic and electrical transport studies in high magnetic fields (5 T) reveal that the addition of Ag into the Gd[sub 0.95]Ba[sub 2]Cu[sub 3.05]O[sub 7-[delta]] (GBCO) enhances the magnetic critical current density (J[sub mc]), volume pinning force (F[sub p]), flux explosion, and transport critical current density (J[sub tc]). Microwave-induced dc voltage studies show the reduction in the total number of weak links between superconducting GBCO grains with increase in Ag concentration. The flux creep rate was also increased with increase in Ag concentration in GBCO resulting in stronger pinning potential. The increase in J[sub mc], J[sub tc], and, hence, F[sub p] with Ag addition in the GBCO suggests the creation of an SNS-type proximity junction at the intergrannular region and stronger Josephson current paths between the superconducting intergrains, which may be due to the physical densification and reduction of the total number of weak links by Ag addition into the GBCOmore » superconducting system. 26 refs., 6 figs., 1 tab.« less

Observation of nonbolometric responses to microwave irradiation on YBaCuO films

Nonbolometric response to 8.3-GHz microwave radiation in the resistive transition region of electron-beam-deposited YBaCuO thin films is distinguished from the bolometric response by their different applied microwave power dependence with the nonbolometric effect dominating the voltage response below the boiling temperature of liquid nitrogen. In the presence of a dc magnetic field, the microwave-induced dc voltage in unbiased films shows an oscillatory behavior as a function of microwave power as well as a polarity reversal depending upon the direction of the dc magnetic field. This behavior is consistent with the electromagnetic response arising from the Josephson vortex motion in the junction regions within these granular films.

Inverse AC Josephson effect in granular superconductors of different Josephson-coupling

The inverse AC Josephson effect in granular samples of niobium powder and powdered as well as sintered YBa 2Cu 3O 7−δ was investigated. The microwave induced DC voltage oscillates with temperature, microwave power, frequency and external magnetic field and depends on the resistivity of the granular material. Utilizing the inverse AC Josephson effect it is possible to detect very small amount of a superconducting phase in a multiphase system.

Inverse AC Josephson effect on multiphased high temperature oxide superconductors

The measurement of the microwave-induced voltage across a granular sample due to the inverse AC Josephson effect provides a technique to detect a superconducting phase in a multiphase system. For the systematic investigation of this technique the authors prepared powder samples from two Y-Ba-Cu-O compounds of different oxygen content and therefore different critical temperature. They measured the microwave induced DC voltage as a function of temperature of varying concentration of the higher Tc compound. External magnetic field, power and frequency of incident microwaves were also varied.

Effects of microwave radiation on YBaCuO films

A systematic investigation of the microwave effects on YBaCuO films show that there are several possible mechanisms involved. By properly coupling an unbiased film to the rf magnetic field, the microwave-induced dc voltage is shown to be oscillatory as a function of microwave power and dc magnetic field as well as to reverse its sign upon changing the magnetic field's direction. These results are in agreement with the nonlinear dynamic responses associated with the Josephson effects.

Dissipative flow of Josephson and Abrikosov fluxons in high Tc superconductors

A model is presented for the field dependent microwave absorption in high Tc superconductors; fluxon motion in Josephson juctions and in bulk material causes the absorption. Junction dissipation is demonstrated by microwave induced dc voltage across YBaCuO samples which has a magnetic field dependence.

Amplitude-dependent velocity of vortices in long Josephson junctions estimated from microwave-induced dc voltages

The microwave-induced dc voltage in long Josephson tunnel junctions in the absence of dc bias currents is studied to obtain the velocity of a moving vortex train driven by a microwave. Detailed experiments for the induced dc voltage are carried out for the experimental configuration where the amplitude and the length of the vortex train can be controlled by the magnitudes of the applied microwave and the dc magnetic field. An analysis of the induced dc voltage is made on the basis of Whitham’s averaged Lagrangian method, which explains well the observed dependences of the induced dc voltage on the microwave power and the dc magnetic field. The velocity of the vortex train is estimated from the observed dc voltage, and is shown to be strongly dependent on the amplitude as is predicted from the theory.

Investigation of Microwave-Induced dc Voltages across Unbiased Josephson Tunnel Junctions

We have studied the power dependence of the microwave-induced dc voltages across unbiased Pb---Pb oxide---Pb Josephson tunnel junctions and found a systematic dependence. We have also found that the Josephson effect in the form of induced quantum voltages was observable in a large dc magnetic field as high as 0.5 kG, about one-half of the ${H}_{c2}$ of the superconducting Pb film.

Microwave-Induced dc Voltage in Bismuth

Received 13 September 1962DOI:https://doi.org/10.1103/PhysRevLett.9.342©1962 American Physical Society