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High quality Nb films were successfully prepared on both flexible polyimide (PI) and rigid Al2O3 substrates and their transport properties were systematically studied at various applied currents, external magnetic fields, and sample orientations. It is found that a curved Nb/PI film exhibits quite different superconducting transition and vortex dynamics compared to the flat Nb/Al2O3 film. For the curved Nb/PI film, smooth superconducting transitions were obtained at low currents, while unexpected cascade structures were revealed in the ρ(T) curves at high currents. We attribute this phenomenon to the gradient distribution of vortex density together with a variation of superconductivity along the curved film. In addition, reentrant superconductivity was induced in the curved Nb/PI thin film by properly choosing the measurement conditions. We attribute this effect to the vortex pinning from both in-plane vortices and out-of-plane vortices. This work reveals the complex transport properties of curved superconducting thin films, providing important insights for further theoretical investigations and practical developments of flexible superconductors.

High-efficiency terahertz (THz) emission and detection are of great interest because of their promising applications in high-speed communications, biomedicine, and imaging. A previous study has achieved efficient room-temperature THz emission at ∼360 GHz by green-light exciting the lattice symmetric stretching vibrations of ZnO nanoplates self-assembled into ZnO microspheres (MSs). Herein, we explore resonant THz radiation of this kind of ZnO MSs under around 360 GHz excitation. A Fabry–Perot resonant cavity is designed and used to obtain the resonant THz signal. Compared to the case without the ZnO MSs, the THz output powers are enhanced by 1.5 and 3.2 times under two excitations of 356.1 and 375.8 GHz with an input power of 6.5 mW, respectively. Furthermore, it is shown that when a wide frequency THz wave irradiates on the ZnO MSs in the cavity, the output THz signal strength shows an obvious variation with frequency and can thus be utilized to detect the presence of some THz waves with specific frequencies. This work indicates that such self-assembled MSs can not only radiate the enhanced THz waves via a resonator, but also effectively apperceive some specific THz signals as a detector.

The tunability in Josephson junctions is foundational to the superconducting classical and quantum applications. Here, we demonstrate the local manipulation of supercurrent realized in a superconducting quantum interference device (SQUID) with two Nb/TiO x /Nb Josephson junctions that is biased at the TiO x layer. Our measurements indicate that the multi-port device allows for an easy and in situ tunability of the supercurrent. The control mechanism can be finely explained by simple yet valid theoretical methods, which take an effective electronic temperature across the SQUID and the self inductive magnetic flux into account. Furthermore, we show that the phase difference and kinetic inductance of this device can be tuned locally via the injection current. Thus, the device provides perspective for several superconducting electronics such as tunable superconducting circuits, sensitive magnetometry, and fast digital elements.

We fabricated thin film Nb/Au/NbSeaamp;lt;subaamp;gt;2aamp;lt;/subaamp;gt; hybrid Josephson junctions by a dry transfer technique with only a single lithography step in the process. A thin Au layer is deposited on Nb to prevent oxidation during the fabrication process. The superconducting van der Waals (vdW) material NbSe2 is placed on top of the Nb/Au layer. Electrical transport properties are studied in detail and are compared to numerical simulations. The current-voltage characteristics we observe are typical for superconductor-normal metal-superconductor junctions and we do not observe an effect of a potential insulating barrier between NbSe2 and Au. The modulation of the critical current in magnetic fields indicates an inhomogeneous distribution of supercurrent density, presumably caused by the roughness of the Nb/Au interface to NbSe2. Nevertheless, we observe clear integer Shapiro steps, indicating a sinusoidal current phase relation of junctions. We do not see an impact of the anisotropic s-wave and the charge density wave in NbSe2 on the Josephson effects. Our method presents a viable and simple way to fabricate hybrid Josephson junctions between superconducting films and two-dimensional (2D) vdW superconducting materials, which might offer a chance for widespread applications.

Tl-based superconducting devices have been drawn much attention for their high transition temperature (T c), which allow the high temperature superconductors (HTS) devices to operate at temperature near 100 K. The realization of Tl-based devices will promote the research and application of HTS devices. In this work, we present transport properties of Tl2Ba2CaCu2O8 (Tl-2212) microbridges across a low-angle step on LaAlO3 (LAO) substrate. We experimentally demonstrate intrinsic Josephson effects (IJEs) in Tl-2212 films by tailoring the geometry, i.e., reducing the width of the microbridges. In the case of a 1 μm width microbridge, in addition to the observation of voltage branches and remarkable hysteresis on the current–voltage (I–V) characteristics, the temperature dependence of differential resistance shows a finite resistance above 60 K when the bias current is below the critical current. For comparison, the wider microbridges are also investigated, exhibiting a highly critical current but do not showing obvious IJEs.

Table tennis is China’s national ball, which leads to education and teaching is particularly important. In the daily teaching of table tennis technical movements, it is difficult for coaches to achieve one-to-one training mode. At the same time, due to the different foundation of students, it is difficult for coaches to teach students in accordance with their aptitude. At the same time, based on the objective factors such as the angle and position of table tennis, the coach’s judgment may be biased, which leads to the realization of 3D table tennis simulation animation based on computer. Through 3D table tennis simulation animation, we can not only improve the shortcomings of traditional table tennis teaching, but also make table tennis teaching more modern. Therefore, this paper first analyzes the movement principle of table tennis. Then, this paper designs the visual servo control system, which can better watch the entity training. Finally, this paper proposes the implementation method.

We design and fabricate λ/2 coplanar waveguide NbN resonators, the thickness and length of which are only several nanometers and hundred microns, respectively. The quality factor of such compact resonators can reach up to 7.5 × 104 at single photon power level at 30 mK with the resonance frequency around 6.835 GHz. In order to tune the resonant frequency, the resonator is terminated to the ground with a dc-SQUID. By tuning the magnetic flux in the dc-SQUID, the effective inductance of the dc-SQUID is varied, which leads to the change in the resonant frequency of the resonator. The tunability range is more than 30 MHz and the quality factor is about 3 × 103. These compact and tunable NbN resonators have potential applications in the quantum information processing, such as in the precision measurement, coupling and/or reading out the quantum states of qubits.

We experimentally studied a series of terahertz (THz) metamaterials with asymmetric resonator structures made from superconducting niobium nitride or gold films. Fano and toroidal dipole resonances are excited in superconducting metamaterials and their quality factors are higher in comparison with those of gold samples. Superconducting samples possess good tuning behaviors for both Fano and toroidal dipole resonance frequencies due to the change of kinetic inductance under different temperatures. The superconducting samples also exhibit good slow light effect due to the sharp dispersion in transmission spectra. These tunable and low loss metamaterials possess great significance to the development of THz nonlinear and slow light devices.

Owing to appealing physical properties such as broad tunability in bandgaps and structural anisotropy, black phosphorus (BP) holds great potential in exploring novel electronic devices. However, it is extremely challenging to use BP to fabricate electronic devices, since it is prone to deteriorate in air. To address this challenge, we demonstrate an in situ fabrication technique which enables us to minimize interfacial degradation and to fabricate vertical Josephson junctions by employing few-layer BP as a barrier between two closely spaced Nb electrodes. The current–voltage characteristics of the junctions are hysteretic at low temperatures and become nonhysteretic when approaching the junction critical temperature. In the resistive state the differential conductance increases with decreasing voltage. Microwave-induced Shapiro steps were observed, confirming the presence of the ac Josephson effect. We present different models to analyze the current–voltage characteristics and conclude that resistive state of the current–voltage characteristics points to a zero bias anomaly, which is presumably caused by Andreev reflections. Our in situ fabrication technique represents a viable way to incorporate air-unstable materials for electronics and offer a chance to explore their unique functionalities.

We investigated the current–voltage characteristics and the critical current density (J c) of a YBa2Cu3O7−δ grain boundary (GB) long Josephson junction with respect to magnetic field (H) under different application directions. When H is rotated within the bc-plane of the film, a small peak of J c is observed when H is parallel to the c-axis, which denotes that there are some residual c-axis dislocations in the GB. When H is rotated within the ac-plane, some vortex-flow steps can be observed in the current–voltage curve at a high inclination angle of H. The vortex-flow step becomes smaller and wider with the decreasing angle between H and the c-axis. These results are a clear demonstration of vortex splitting at the GB plane in YBa2Cu3O7−δ GB long Josephson junctions.

We report an experimental observation of the macroscopic quantum tunnelling (MQT) in a d-wave high-temperature superconductor (HTSC) Bi2Sr2CaCu2O8+δ intrinsic Josephson junction (IJJs). It is well known that the current-biased Josephson tunnel junction provides an ideal stage for studying a variety of macroscopic quantum phenomena such as MQT. They have been studied and observed in low-temperature superconductor (LTSC) Josephson junctions since the early 1980s and have been established well by now. On the other hand, in the case of HTSC the d-wave pairing symmetry allows for dissipative quasiparticle excitations within the superconducting energy gap, which is expected to severely interfere with an observation of MQT. Contrary to this naive conception, our experimental results have explained that the effects of the nodal quasiparticles are not strong enough to obscure the observation of the MQT. Furthermore, we found that the MQT in IJJs was observed at approximately 1 K, which was ten times higher than that of LTSC Josephson junctions. This higher classical-to-quantum crossover temperature is due to their high plasma frequency. We also discuss the resonant activation of IJJs in the presence of microwave radiation.

To investigate the detailed junction properties of intrinsic Josephson junctions (IJJs) in YBa2Cu3O7−X (YBCO) without shunted grain boundaries and with good uniformity, we fabricated sub-micron sized IJJs in a YBCO whisker by using a focused-ion-beam etching. The sub-micron sized junctions showed clear multiple branches with a hysteresis structure in the current–voltage curve, like IJJs in Bi2Sr2CaCu2O8+X. The temperature dependence of the critical current demonstrates that the junction behaviour drastically changes from that of an SNS type to an SIS type when the critical temperature is decreased. The critical current density of the junctions, in the order of 10–100 kA cm−2, corresponds to Josephson plasma frequencies from a few hundred GHz to 1–2 THz.

With a novel double-sided fabrication method, stacks of intrinsic Josephson junctions (IJJs) superconductively connected to each other can be patterned and integrated with other circuits. On a slice of Bi2Sr2CaCu2O8+x (BSCCO) 200–300 nm thick, over an area of 500 × 420 µm2, so far we are able to fabricate up to 2500 stacks. A single stack with submicrometre lateral sizes has already been obtained without observable degradation. Zero-crossing and non-zero-crossing Shapiro steps have been observed under irradiation from a far-infrared laser. Thus, quite a few good electronic devices can be built based on IJJs operated at relatively high temperatures and over a wide frequency range.

Using YBa2Cu3O7/MgO bicrystal Josephson junctions operating between 6–77 K, we have studied their responses to monochromatic electromagnetic radiation from 50 GHz to 4.25 THz. We have obtained direct detections for radiation at 70 K from 50 GHz to 760 GHz and at 40 K from 300 GHz to 3.1 THz. This indicates that fast detectors can be realized to cover the 10:1 frequency band at one operation temperature, and about 100:1 can be covered by operating only one junction at two different temperatures. Both the highest response frequency and the maximum value of the normalized response are shown to be proportional to the ICRN product of the junction, where IC and RN are the critical current and the normal resistance of the junction, respectively.

We studied the motion of fluxons in a stack of intrinsic Josephson junctions (IJJs) of Bi2Sr2CaCu2O8+δ single crystals in a long junction limit. Driven by the tunnelling bias, current Josephson fluxons excite plasma oscillations and move in resonance with the plasma propagation modes. We examined two types of samples in this study; mesa structure (UD1) and a stack of junctions sandwiched between normal-metallic electrodes (DSC1). In a high magnetic field, the hysteresis in the I–V characteristics of both-types of samples vanished. The resulting single I–V curve exhibited a cusp structure at characteristic bias voltages which were believed to be boundaries of different moving fluxon configurations. We studied the sample-geometry dependence of the cusp characteristics by comparing the results from the two types of samples.

The propagation of an electromagnetic wave in a stack of superconducting layers, which are separated by interleaving layers while still coupled closely to each other, is analysed based on the dispersion relation obtained by matching the tangential components of the fields, or, more easily, by using the 'transverse resonance' procedure. A stack of Josephson junctions, where the interleaving layers are thin insulators so that each pair of adjacent superconducting layers form a Josephson junction, is treated as an example, revealing that the thickness of the top and bottom layers plays an important role in determining the propagation while the effects of the normal metals as electric leads are negligible.

In this paper, we report on the recent progress in fabrication and high-frequency experiments of Bi2Sr2CaCu2O8+x (BSCCO) intrinsic Josephson junctions (IJJs). Using a newly developed double-sided fabrication process, we single out a well-defined number of IJJs in a well-defined geometry from inside a slice of a BSCCO single crystal. We discuss in detail the observations of both Shapiro steps and harmonic mixings in the terahertz region, and we indicate the possible applications in spectroscopy.

We propose a new method for fabricating resistively shunted intrinsic Josephson junctions (RS-IJJs). Two mesas, measuring 6 × 6μm2 and 100 × 100 μm2 respectively in the a-b plane, have been fabricated in a Bi2Sr2CaCu2O8+x single crystal with a SiO layer evaporated in-between as an insulator. A gold stripe was sputtered onto the insulator to connect the mesas, thus effectively shunting the smaller one. The current–voltage (I–V) curves of such RS-IJJs have shown the typical behaviour of a resistively shunted junction with greatly reduced hysteresis and voltage jump. Under microwave irradiation at a 3 mm waveband, we have registered three types of Shapiro steps: conventional, sub-harmonic and zero-crossing. In this rapid communication, we discuss the fabrication details, as well as the observations of the Shapiro steps.

We studied the grain boundaries within mechanically formed polycrystalline BaKFe2As2 micro-bridges. By tunneling current across grain boundaries, current–voltage characteristics (IVCs) demonstrated the typical Josephson weak links behavior in micro-bridges. Shapiro steps were observed for the junctions under the microwave radiation at 10 GHz. The temperature dependence of the critical current I c was observed as a shoulder, corresponding to a multi-gap symmetry but not a single-gap s-wave or d-wave.

Emission of terahertz (THz) electromagnetic (EM) waves from a high critical temperature (T c) superconductor intrinsic Josephson junction (IJJ) is a new and promising candidate for practical applications of superconducting devices. From the engineering viewpoint, the IJJ THz source is competitive against the present semiconducting THz sources such as quantum cascade lasers (QCLs) and resonance tunnelling diode oscillators because of its broad tunable frequency range and ease of the fabrication process for the device. The emitted EM waves are considered to be coherent because the emission is yielded by synchronisation of thousand stacked IJJs consisting of the mesa device. This synchronisation is peculiar: the resonant frequency of each IJJ is distributed because the cross section of the mesa device is trapezoidal in shape. One of the key features of the synchronisation mechanism is the temperature inhomogeneity of the emitting device. In this topical review, we describe the recent progress in studies of IJJ THz sources with particular emphasis on the relevance of the temperature inhomogeneity to the synchronisation and the emission intensity. This review is of specific interest because the IJJ THz source shows the rich variety of functions due to self-heating which has always been a detrimental feature in the present superconducting devices. Moreover, the thermal managements used for IJJ THz sources will be common with those of other semiconducting devices such as QCLs. In addition, this review is to invite the readers into related research through the detailed descriptions of experimental procedures.

Sensitivity of high temperature superconducting (HTS) Josephson detectors at millimetre-wave band has been studied in detail. YBCO grain boundary Josephson junctions with the normal-state resistance (RN) around 1 Ω and ICRN product of less than 2 mV have been fabricated for this study, where IC is the critical current of the junction. A Gunn oscillator at the frequency of 98 GHz together with a set of calibrated attenuators with a total attenuation of 90 dB are used as a signal source. A quasi-optical system, which consists of a wideband planar log-periodic antenna encompassing the junction, parabolic mirrors and a hyperhemispherical silicon lens, has been used as an effective coupling system. Sensitivity increases with ICRN. Using a junction with ICRN of 300 µV, a sensitivity of about 9000 V W−1 has been obtained, which is higher than that of the Schottky diode detectors at the same frequency band and demonstrates that the HTS Josephson detectors are very sensitive at millimetre-wave band.

Recently, we experimentally demonstrated that rectangular mesa structures of intrinsic Josephson junctions (IJJ) in Bi2Sr2CaCu 2O8+d (Bi2212) can be used as a compact solid-state generator of continuous, coherent and polarized terahertz (THz) radiation. In the present work, we will exhibit tall mesas (over 600 junctions) which were fabricated using UV lithography, e-beam lithography with photoresist and e-beam lithography with a Ti selective etching technique. We will present measurements of the c-axis resistance as a function of temperature and of current-voltage characteristics of THz emitting mesas with lateral sizes ranging from 30 × 300 to 100 × 300νm2. Furthermore, we will discuss the dependence of the characteristics of the mesa structures on the oxygen doping level of the Bi2212 crystals. We will also experimentally show that the voltage-frequency relation of the ac Josephson effect has to match the cavity resonance for successful emission., TÜBİTAK project no. 108T238 and US Department of Energy, Basic Energy Sciences-Materials Sciences, under contract no. DE-AC02-06CH11357

A mesa with a-b plane dimensions of 12 ?m ? 12 ?m was patterned on Bi2Sr2CaCu2O8 single crystal, after which two separate electrical contacts were carefully fabricated on the top of the mesa to ensure a standard four-probe arrangement. With contact resistance excluded, the measured current-voltage (I-V) curves featured high voltage resolution. Voltage jumps up to 20 mV and remarkable hysteresis at 4.2 K indicated typical superconductor-insulator-superconductor properties. A few sharp current steps started to manifest themselves clearly when a magnetic field of about 10 kOe was applied parallel to the a-b plane. Carefully studied were the dependences of the current steps on the magnetic fields and the operating temperatures. We attributed the field-induced steps to the flux-flow resonances, and the multisteps implied different modes existing in the stacked intrinsic junctions. The voltage region at which the steps occurred was of the order of millivolts, indicating possible high-frequency applications at mm and sub-mm wavebands.

The effect of a grain boundary (GB) in YBa2Cu3O7−δ thin films for guiding vortex motion is studied by investigating transversal (Hall) and longitudinal magnetoresistances, (Rxy) and (Rxx). Here, a GB is inclined to the direction of the applied current with an angle of 30°. We investigate the dependences of both Rxy and Rxx on the temperature, the applied magnetic field and the bias current. It is found that the GB can act as an easy-flow channel for vortex motion. Furthermore, the pinning force in a GB is also discussed.

Using a high- superconducting harmonic mixer at 77 K and a phase-locking loop, a signal source (a Gunn oscillator in the 3 mm waveband) was directly phase-locked to a local oscillator for frequencies less than 1 GHz and harmonic numbers up to 120. The phase-locked Gunn oscillator achieved a frequency instability of less than Hz, with the counting time of 1 s, while the phase noise at intermediate frequency 40 MHz was ( kHz) for 120th harmonic mixing and ( kHz) for 42nd harmonic mixing. The output of this phase-locked signal source was applied to a Josephson junction array used in a voltage-standard system against which a solid-state voltage source (a Zener voltage reference) was measured. The experimental results showed that the quality of this phase-locked microwave source was good enough to justify its use in the quantum voltage standard.

A Superconducting Integrated Receiver (SIR) comprises on one chip all elements needed for heterodyne detection. Light weight and low power consumption combined with nearly quantum limited sensitivity and a wide tuning range of the superconducting local oscillator make SIR a perfect candidate for many practical applications.

Recent progress in terahertz technology has enabled precise investigation of the ultrafast dynamics of excited carriers, nonequilibrium state and nonlinear response of superconductors, resulting in the proposal of novel optoelectronic device applications based on such ultrafast perturbation of supercarriers in the terahertz frequency region. In this paper, we focus on exploratory research in the field of superconductor terahertz science and technology, and present a review of superconducting terahertz sources and the response of superconductors excited by ultrashort electromagnetic pulses, including optical pulses and high-intensity THz pulses.

Terahertz (THz) emission has been recently detected from intrinsic Josephson junction (IJJ) stacks made of the high critical temperature superconductor Bi2Sr2CaCu2O8+? (BSCCO). The most employed structure is a mesa standing on a big pedestal of a single crystal with a thin gold layer as its top electrode. In this work, a large (300???50???1.2??m3) IJJ stack with superconducting electrodes was fabricated and studied. The stack consisted of N???800 IJJs. It was prepared with a double-sided fabrication process, and significant THz emission was detected. The output power is comparable to the emission power detected from mesa structures, obviously not weakened by the superconducting upper electrode. The observation of THz emission from the double-sided structure suggests that off-chip THz emission from IJJs can be obtained not only from mesa structures and, most importantly, that the emission power can be potentially enhanced in integrated multi-stack radiation sources.

In this work twin-free tetragonal NdBa2Cu3O7?? films were fabricated that exhibited superconductivity with sufficient anisotropy which produced intrinsic Josephson junction (IJJ) characteristics in the films. The intrinsic Josephson effects (IJEs) were observed in oxygen-deficient single-crystalline NdBa2Cu3O6.65 (NBCO) films grown on SrTiO3 (STO) substrates, using tri-phase epitaxy (TPE). The single-crystalline nature of NBCO films on well-matched STO substrates, and the precisely controlled oxygen content of the films, lead to the IJEs of the thin films. Furthermore, the films exhibit high anisotropy and clear multiple-branch structures, with hysteresis observed in the current?voltage characteristics. Periodic Josephson vortex?flow resistance oscillations were also observed for a magnetic field higher than 64?kOe, which was applied normal to the junctions. These results strongly support the single-crystal nature of TPE films, which play an important role in both the fundamental study and the practical applications of high-frequency devices.

Single-crystal whiskers of Y1Ba2Cu3O x with a length of approximately 4 mm were grown from an Sb-doped precursor. The optimum nominal composition of precursors in this Sb-doping method is Y2Ba2.75Cu3Sb0.5O x . Sb is not detected in the whiskers by energy-dispersive X-ray spectroscopy. The standard 4-probe transport measurements for the as-grown whiskers show a critical temperature T C of approximately 90 K and a c-axis critical current density J C of 6.57 ×104 A/cm2 at 89 K.

The lock-in phenomena of Josephson vortices have been studied under the vicinal layer parallel magnetic field in a field cooling experiment. As a sign of the lock-in state, Josephson vortex-flow voltage was measured with c-axis bias current in an in-line type intrinsic Josephson junction formed on a single-crystal Bi2Sr2CaCu2O8+δ superconductor. On cooling, vortex-flow voltage appears at the lock-in transition of the vortices which takes place at the temperature T when the lower critical field H c1(T) grows as high as the c-axis component of the magnetic field. This can be understood as the pancake vortices being expelled from the superconducting double CuO2 layers by the Meissner effect. The temperature dependence of H c1(T) was observed by the lock-in transition at various offset angles.

This paper investigates the temperature dependence of microwave surface resistance (R S) of YBa2Cu3O7-x (YBCO) thin films with different microstructures at 10 GHz, using a coplanar resonator technique. YBCO thin films with different grain sizes were obtained as a result of changing the quenching procedure after film deposition by dc sputtering. The value of R S was found to vary with varying surface morphology and can be explained by the coupled grain model (CGM) when a temperature-dependent grain boundary resistance (R) is used. The temperature (T) dependence of R is given by R=R 0+C(T/T C)2 T, where T C is the superconducting critical temperature, and R 0 and C are the fitting parameters, depending on the properties of each sample.