Nonbolometric Response Research Articles

Response of Granular La1− xCaxMnO3 Film to 10 GHz and 35 GHz Frequency Electromagnetic Radiation

The nonbolometric response of La1 − xCaxMnO3 film to 10 GHz and 35 GHz frequency electromagnetic radiation is investigated in the case when, in addition to the strong electric field of the wave, the film is subjected to a stationary electric bias field. Dependences of responses on the radiation power P at temperature T = 80 K are presented. In the low power region, a linear dependence of the response on P is observed at both frequencies whereas for high powers the dependence behaves as ~P 1/2. The obtained results are explained taking into account that the nonbolometric response originates from the intergranular junctions that operate in the reverse current regime. There two effects take place: (i) at low powers the detection resistance decreases with increasing power P, and (ii) at higher powers in addition to that the film resistance decreases as P 1/2 due to the avalanche of charge carriers in the electric field of the electromagnetic wave.

ミリ波照射時におけるスロットアンテナ結合ＹＢａ２Ｃｕ３Ｏ７‐δマイクロブリッジの応答機構と速度

The study of nonbolometric responses caused by the vortex motion and other factors of YBa2Cu3O7-δ (YBCO) microbridges has received much attention because of possible applications for sensitive and fast response detectors. In this study, we fabricated a slot antenna-coupled YBCO microbridge and investigated IF properties at 94 GHz to evaluate the response speed of the device in the resistive state. The response mechanism of the device biased in the resistive state consists of the bolometric response and the nonbolometric response caused by the flux creep and flux flow. From the measurements of voltage-current (I-V) characteristics and video detection properties, the response mechanism was investigated and operating conditions that dominated the bolometric and nonbolometric responses were obtained. The IF bandwidth of the device, having its response dominated by the bolometric process, showed a constant value of about 60 MHz and did not depend on the bias current. On the other hand, the bandwidth dominated by the flux flow response increased as the bias current and temperature increased, up to 1.2 GHz, and depended on the vortex velocity.

Flat coil-based tunnel diode oscillator enabling to detect the real shape of the superconductive transition curve and capable of imaging the properties of HTSC films with high spatial resolution

Owing to a pick-up coil's flat design, relatively low MHz-range operation frequency, and six orders relative resolution a flat coil-based tunnel diode oscillator has advantages, compared to all other methods. They become crucial in studies with thin high-Tc superconductivity (HTSC) materials (with small signals), especially at the start of the Cooper pairs’ formation. Due to this the superconductivity precursor ‘paramagnetic’ effect was detected recently in YBaCuO films at N/S transition. It precedes Meissner ejection and specifies details of the shape of the transition curve. We discuss the influence of the currents on this effect, and the relationship between the quality of the material and the shape of the effect. A new imaging device has also been created based on this test method (using a focused He–Ne laser beam as a probing signal), capable of imaging the properties of HTSC films with ∼3μm spatial resolution. The method is based on detection of the inductance and Q-factor value changes of a single-layer flat coil, placed at the face of the sample. This leads to frequency and/or amplitude changes of the stable oscillator. The test device enabled 2D-mapping of the grain structure of a bridge-shaped YBaCuO film. Basically, the method is capable of imaging 2D-current distribution in thin HTS with sub-μm spatial-resolution, using non-bolometric response. However, the achieved resolution ∼3μm of a bolometric nature (in a given device with 3.5mm-size coil) by no means is limited by the abilities of the method, but mainly, it depends on how narrowly it is possible to focus the probing beam, while the own resolution of a present flat coil-based technique is better than 0.1μm, and can be improved essentially by reducing the coil size.

Detection properties of slot antenna coupled YBCO microbridges based on vortex motion

High-T/sub c/ YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) microbridges coupled to a slot antenna were fabricated and the video detection properties in the resistive state were investigated under the irradiation of 94 GHz millimeter-waves. A detected voltage dominated by the nonbolometric response due to vortex motion was observed in the vicinity of the critical temperature. From measurements of the polarization dependence of the detected voltage, it was found that the detected voltage, based on the vortex motion, was not due to the photon energy but instead to a high frequency current induced in the antenna. I-V characteristics of the device with and without the external magnetic fields were also measured. Detected voltages increased with the vortex velocity and the maximum detected voltage was obtained when the vortex velocity was at its maximum.

抵抗性状態における高温超伝導ＹＢａ２Ｃｕ３Ｏ７‐δマイクロブリッジのミリ波検出特性

Slot antenna-coupled high-Tc YBa2Cu3O7-δ(YBCO) microbridges were fabricated and their millimeter-wave detection properties in the resistive state were investigated at 94 GHz. The nonbolometric response due to vortex motion was observed in the vicinity of the critical temperature. It became dominant in the extended temperature region when the bias current was increased. The detected voltages were almost proportional to the vortex velocity in the microbridge and the maximum voltage was detected when the vortex velocity was at its maximum. We have shown that the nonbolometric response is obtained by enhancement of the vortex motion due to the high frequency current induced by the slot antenna. Keeping the bias current constant, the detected voltages were almost proportional to the input power, and a responsivity of approximately 180 V/W was obtained.

IF properties of YBCO hot-electron bolometer mixers for millimeter-wave radiation

Slot antenna coupled YBa 2Cu 3O 7− δ (YBCO) hot-electron bolometer mixers for 94 GHz millimeter-wave radiation were fabricated. Temperature dependencies of the detected voltage and the temperature derivation of the resistance (d R/d T) were measured in the video detection at 94 GHz. The detected voltage dominated by the bolometric effect, which was proportional to the d R/d T, was obtained. On the other hand, the nonbolometric response, which was caused by the flux creep effect, was also observed in the vicinity of the critical temperature ( T c). In the heterodyne mixing at 94 GHz the IF bandwidth of the device, whose response was dominated by the nonbolometric process, was about 1.0 GHz. This value was higher than that of the YBCO bolometer mixer whose response was dominated by the phonon escape time.

Response of superconducting Y–Ba–Cu–O films to millimeter wave radiation

The origin of temperature and radiation power response dependencies to millimeter wave radiation is analyzed for Y–Ba–Cu–O thin films. These dependencies were both experimentally measured and described by an empirical formula. The results which were obtained indicate that the peak shape of temperature dependence for the nonbolometric response is determined by the temperature of the thermostat and is less inertial than for τ=1/f (f=35 GHz).

Slot antenna coupled YBa 2Cu 3O 7− δ hot-electron bolometers for millimeter-wave radiation

Slot antenna coupled YBa 2Cu 3O 7− δ (YBCO) hot-electron bolometers for 94 GHz millimeter-wave radiation were fabricated. The video detection was carried out in order to investigate response mechanisms of fabricated devices. The bolometric response was dominant at temperatures from the transition region to the normal state. However, the nonbolometric response due to the flux creep was also observed in the vicinity of the critical temperature ( T c). When increasing the bias current, the nonbolometric response was dominant. The mixing property of the device, which was dominated by the bolometric response, was also measured. The YBCO bolometer mixer with the phonon diffusion time of about 0.65×10 −9 s was realized in the heterodyne mixing at 94 GHz.

Low-temperature scanning laser microscopy of individual filaments extracted from (Bi, Pb)2Sr2Ca2Cu3O10+x tapes

The method of low-temperature scanning laser microscopy is applied to visualize the resistive state in individual superconducting filaments extracted from (Bi, Pb)2Sr2Ca2Cu3O10+x/Ag tapes. This technique is capable of imaging the distributions of the critical currents over a sample. Using the nonbolometric response, a spatial resolution of about 1 μm is demonstrated for 10-μm-thick filaments. Some of the resistively visualized grain boundaries between crystallites show Josephson behavior.

Observation of bolometric optical response in superconducting microwave meander lines

The change in the resonant frequency of YBa2Cu3O7−x meander lines under thermal and optical perturbations was used to determine whether pair breaking effects are induced either by bolometric or nonbolometric responses. The frequency-domain measurements were performed by monitoring the change of both the microwave resonance mode frequency and frequency width. The variation of the resonant frequency induced by two external perturbations shows a quadratic dependence on each perturbation in the range of 0.28Xc–0.56Xc. A perturbation to the fourth dependence is observed above 0.63Xc, where Xc is either the critical temperature or the critical optical pulse energy at which resonance can no longer be distinguished. The results suggest that the photoresponse of the superconducting meander line is bolometric due to laser heating.

Infrared Radiation Detector with YBa2Cu3OX Thin Film

We investigated an infrared (IR) radiation detector using a c-axis oriented YBa2Cu3OX thin film with a microbridge structure. The photoresponse was measured under IR radiation and was found to depend on the bias current. A bolometric response was observed under relatively low bias current, which was inversely proportional to the square root of the modulation frequency of IR irradiation. The frequency dependence can be explained by a heat diffusion process that is similar to that of a microbolometer. With increasing bias current, a nonbolometric response was observed just above the superconducting transition temperature (Tc). This was caused by the enhancement of additional flux creep induced by modulated IR light, which was equivalent to an increase in resistance. The maximum responsivity and noise equivalent power (NEP) were 1.7×104 V/W and 2.1×10-14 W/Hz1/2, respectively.

Response of high-temperature superconductors to electromagnetic radiation: (A Review)

Nonequilibrium processes resulting from the interaction of high-temperature superconductors with electromagnetic radiation are considered from microwave to optical range. Emphasis is laid on the dependence of surface or dc resistance on external parameters (temperature, bias current, modulation frequency, magnetic field, radiation power, and frequency), which is characteristic of every nonbolometric response mechanism considered by us. The most frequently used methods for monitoring the response of HTSC to electromagnetic radiation are described.

YBa2Cu3O7/noble metal composite thin films for applications in fluxonic and flux-flow devices

This research involves the study of thin films for use in three-terminal, non-linear two-terminal, and photodetector superconducting devices. The morphological and electrical properties of composite films fabricated from YBCO and noble metals have been investigated for use in these devices. Films of Ag and Au, when heated to YBCO deposition temperatures, coalesce into small, approximately micron-sized islands. We take advantage of this property to form a composite film with distinct YBCO and noble metal regions by depositing a layer of YBCO on the array of noble metal islands. With certain compositions the films exhibit reduction of critical current density by a factor of 65 over YBCO and show no significant degradation of critical temperature. Also, the current-voltage characteristics of the composites are sensitive to small, applied magnetic fields. These properties make the YBCO/noble metal composites potentially well suited for the fabrication of devices whose transport is dependent upon vortex motion. Photoresponse measurements taken on a 1 mm × 1 mm YBCO/Au bridge irradiated by red laser light showed a possible non-bolometric response below the composite superconducting transition temperature.

Simultaneous bolometric and nonbolometric microwave response in biepitaxial Y-Ba-Cu-O thin films

Measurements and the modeling of the microwave (9 GHz) response of a biepitaxial thin film showing the simultaneous presence of bolometric and nonbolometric response peaks in the same sample are reported. The nonbolometric response in this Y-Ba-Cu-O thin film gives further evidence of microwave detection in the networks of inherent Josephson junctions present at the grain boundaries between two epitaxial layers. By modeling the film as a distribution of granular connections with varying critical currents and temperatures we achieve results similar to those observed in microwave response measurements in granular Bi-Sr-Ca-Cu-O thin films.

Optical response of single crystal and bicrystal YBa 2Cu 3O 7−δ thin films

We have investigate the optical response of YBa 2Cu 3O 7-δ grain boundary junctiond as well as single crystal strip lines. For both devices, bolometric siganal was detected between T c(zero) and T c(onset), whereas nonbolometric signal was observed only in a temperature range just above T c(zero) where the current-voltage characteristic showed nonlinear behavior. The content of nonbolometric signal in the total response signal was remarkably increased with decreasing the film thickness. The effect of a single grain boundary on the nonbolometric response was described.

Photoresponses of granular (Pb)BiSrCaCuO films to millimeter wavelength radiation

The photoresponses of Pb doped 2223 phase BiSrCaCuO films to low power 5 mm cw radiation were measured at temperatures near Tc. To identify the involved detection mechanisms, dependence of responsivity on temperature, supplied current, radiation power, and film granularity were investigated. At temperatures in the vicinity of the transition to the normal state, good agreement was obtained with the responses derived from a bolometric model. At temperatures below the transition, a nonbolometric response mode was found to occur when the film was biased into a partially resistive regime. Transient measurements were carried out showing a response time for this mode of at least 5 orders of magnitude smaller than that of the bolometric response. Further characteristics inherent to the nonbolometric mode include square law detection, nonlinear current dependence, and short wavelength cutoff. In addition, a correlation between responsivity and film granularity was established. For strongly granular films with an active area of 300×1800 μm2, a detectivity D* of about 1.1×108 cm Hz1/2/W was typically achieved at a modulation frequency of 5 kHz. Consistency of the experimental results with the sub-gap responses of Josephson arrays is discussed.

Model of the microwave response in granular Bi-Sr-Ca-Cu-O thin films

A model used to approximate the measured response of a Bi-Sr-Ca-Cu-O detector to both microwave frequency and HeNe laser light over a temperature range from zero up to the critical transition temperature of the superconductor Tc is reported. The nonbolometric (microwave) response model is based on microwave enhancement of a thermal fluctuation voltage occurring in the networks of inherent Josephson junctions. Modeling the film as a distribution of granular connections with varying critical currents and temperatures yields results similar to those observed in recent microwave response measurements. These results may be useful when optimizing the nonbolometric response for detector applications.

A comparison of the nonbolometric microwave response with the bolometric optical response of Tl- and Bi-oxide superconductors

The distinction between the bolometric and nonbolometric responses of high-T/sub c/ Tl- and Bi-oxide superconducting thin films is presented by comparison of the characteristics of the responses at different temperatures and chopping frequencies. The bolometric optical response of the films is proportional to the dR/dT of the films; experimentally, the peak optical response decreases as the chopping frequency of the radiation is increased. The nonbolometric response is not proportional to the dR/dT of the films, and the peak microwave response was found to be almost independent of the chopping frequency. It is found that both components can be observed in the microwave response of a superconducting epitaxial film. The optical response of a continuous-wave (CW) He-Ne laser is mainly due to the bolometric effect, whereas the microwave response using a 34.5-GHz Gunn diode microwave generator is predominantly nonbolometric.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optically triggered switching of optically thick YBCO films

Thin films of high-T/sub c/ superconducting material were used to construct two different types of opening switches: the photoresistive switch and the inductively coupled switch. The former show two distinct switching components in 8000-AA films consisting of a slow bolometric response and a faster nonbolometric response. The fast nonbolometric component had risetimes of approximately 4 ns and falltimes of approximately 6 ns. The slower component was identified to be thermal in origin and was in good agreement with the one-dimensional heat flow model used to simulate the thermal photoresponse. The inductively coupled switch is a contactless switch where the superconducting film screens the flux coupling between two coils of a transformer. The optically induced switching was achieved with risetimes of approximately 50 ns. with a multiturn output coil. Short (150-ps) laser pulses containing energies of up to 3 mJ are used in both cases to perform the switching.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electrical responses of high-Tc superconducting thin films to infrared radiation

The electrical responses to both CW and pulsed infrared radiation of highly oriented thin films of various high- T c oxide superconductors, LnBa 2 Cu 3 O y , La 2−x Sr x CuO 4 , and Ba 1−x K x BiO 3 have been investigated. All films show a clear deviation of the normalized response δV /( dV / dT ) irom a constant value at temperatures below T c which indicates the existence of a nonbolometric response. The responsivity and the normalized response of these materials as well as of BaPb 1− x Bi x O 3 are approximately inversely proportional to the Cooper pair density. These materials show a typical response time of 1 – 10 ns to pulsed radiation. These results can be explained on the basis of the nonequilibrium gap suppression model where the effective quasiparticle recombination time is dominated by the phonon escape time.