Intrinsic Josephson Junction Arrays Research Articles

Phase slips and metastability in granular boron-doped nanocrystalline diamond microbridges

A phase slip is a localized disturbance in the coherence of a superconductor allowing an abrupt 2π phase shift. Phase slips are a ubiquitous feature of one-dimensional superconductors and also have an analogue in two-dimensions. Here we present electrical transport measurements on boron-doped nanocrystalline diamond (BNCD) microbridges where, despite their three-dimensional macroscopic geometry, we find clear evidence of phase slippage in both the resistance-temperature and voltage-current characteristics. We attribute this behavior to the unusual microstructure of BNCD. We argue that the columnar crystal structure of BNCD forms an intrinsic Josephson junction array that supports a line of phase slippage across the microbridge. The voltage-state in these bridges is metastable and we demonstrate the ability to switch deterministically between different superconducting states by applying electromagnetic noise pulses. This metastability is remarkably similar to that observed in δ-MoN nanowires, but with a vastly greater response voltage.

Simulation of THz oscillations in an intrinsic Josephson junction array

When a voltage is applied to coupled Josephson junctions, an ac current flows because of the Josephson effect. Due to this ac current, an electromagnetic (EM) wave is emitted from junctions. For the cuprate High-Tc superconductor, frequency of the EM wave reaches to the THz regime since the energy gap is large. In order to simulate the EM wave in the superconductors, we solve the Josephson junction relations and the Maxwell equations simultaneously. Especially, we consider coupling of junctions including capacitive and inductive couplings, and spatial variations of phase differences of order parameters inside of junctions. We shows time developments of distributions of the phase differences, magnetic and electric fields in junctions in the transient state.

Terahertz Waves Emission From Two <formula formulatype="inline"><tex Notation="TeX">$\hbox{Bi}_{2}\hbox{Sr}_{2} \hbox{CaCu }_{2} \hbox{O} _{8}$</tex></formula> Mesas in Series

The dependence of terahertz (THz) emission power on the thickness of series Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> (BSCCO) mesas is studied in this letter. An intrinsic Josephson junction (IJJ) array with two BSCCO mesas in series is proposed. The current-voltage characteristics of the IJJs, the powers, and Fourier spectra of the THz emission are measured for different thicknesses of the mesas, which is gradually mounted by the argon ion beam milling. Experiment results indicate that the THz emission power grows as the thickness of the mesas is increasing. The power reaches a maximum value of about 0.502 μW at a frequency of 0.708 THz when the thickness is 1200 nm. However, the THz emission power decreases while the thickness of the mesas keeps increasing. This nonlinearity between the THz emission power and the thickness of the mesas is due to the cavity resonance of the mesas and the self-heating generated by the IJJs in the mesas. The structure of connecting two mesas in series can be extended to form an IJJ array of multiple series mesas, which could further improve the THz emission power.

Frequency Characteristics of Misaligned Tl2Ba2CaCu2O8 Thin-Film Intrinsic Josephson Junction Arrays Irradiated by Millimeter-Wave

We have investigated the millimeter wave irradiation characteristics of misaligned Tl2Ba2CaCu2O8 thin-film intrinsic Josephson junction arrays at a liquid nitrogen temperature in an antenna system by both simulation and experiments. The dielectric substrate was regarded as a dielectric resonance antenna to improve high-frequency electromagnetic coupling between the intrinsic Josephson junction array and a horn antenna. A useful model for simulating the microwave system was devised to demonstrate and analyze the optimization of the irradiation in the antenna system. The electric field distribution in the antenna system was computed and displayed. Also, the near-field and far-field frequency characteristics of the receiving antenna and transmitting antenna were calculated and analyzed to study the mechanism of the irradiation. In the experiment, by detecting the suppressed critical current of the IJJA, an optimum transmission frequency range was measured and the frequency characteristic was studied in the transmitting and receiving antenna system. The critical current of the IJJA was suppressed to 37 % and the optimum coupling effect was achieved at 74.8 GHz. And the electromagnetic simulation matched up well with the experimental result. Potential reasons of the acceptable nuances between the simulation and experiment results were also taken into account. The influence the size of the microbridge had on the frequency characteristic of the dielectric antenna were elaborately discussed.

An Effective Method for Improving Emissions from Intrinsic Josephson Junction Arrays of Misaligned Tl2Ba2CaCu2O8+δ Thin Films

In this paper, an effective method for improving emissions from Josephson junction arrays was proposed. We took the substrate as a dielectric resonance antenna to improve the coupling of intrinsic junctions to electromagnetic waves. Electromagnetic simulations were performed in parallel with experiment investigations. Sharp radiation peaks at 76.9 GHz were detected from intrinsic Josephson junction arrays in misaligned Tl2Ba2CaCu2O8+δ thin films at 78 K. Experimental results proved the effectiveness of this method, which offered a competitive choice for coherent emission from intrinsic Josephson junction arrays.

Self-emission from intrinsic Josephson junction arrays in misalignedTl2Ba2CaCu2O8 + δ thin films at 78 K

We report off-chip self-emission at 76.9 GHz from intrinsic Josephson junction arrays in misalignedTl2Ba2CaCu2O8 + δ thin films at 78 K. The substrate was considered as a dielectric resonator antenna toimprove the coupling between arrays and electromagnetic waves. Three-dimensionalnumerical simulations were performed to guide and explain the experiments. Sharpradiation peaks with a maximum radiation power of 17.7 pW were observed. Furthermore,we investigated the angular dependence of the radiation power in terms of experimentcombined with numerical simulations.

Emission of terahertz electromagnetic waves from intrinsic Josephson junction arrays embedded in resonance LCR circuits

The emission of terahertz electromagnetic waves from an intrinsic Josephson junction array (IJJA) embedded in an $\mathit{LCR}$ resonant circuit is studied theoretically. A bias current is applied to the electrodes at the top and bottom of the array. In the voltage state, the ac Josephson current generates a displacement current in the IJJA, and both the currents induce an oscillating current in the electrodes. We describe the whole system, including the array and the environment around it, in terms of an $\mathit{LCR}$ resonant circuit. When the Josephson frequency is in the resonance frequency region of the $\mathit{LCR}$ circuit, the amplitudes of the displacement current in the Josephson junction array and the oscillating current in the electrodes both are strongly enhanced by a feedback process. We calculate the emission power and the current-voltage (I-V) characteristic curve for the system. Inside the frequency region of the $\mathit{LCR}$ circuit resonance, stable and intense emission occurs in both the increasing and decreasing processes of the high-bias current. In the emission region the I-V characteristic curve has a dip structure. These results are consistent with those of the emission observed in a high-bias current region by using mesa-shaped samples of Bi${}_{2}$Sr${}_{2}$CaCu${}_{2}$O${}_{8+\ensuremath{\delta}}$. We also discuss the difference between the properties of the emission and the I-V characteristic curve for intrinsic Josephson junctions embedded in and shunted by the $\mathit{LCR}$ resonant circuit.

Experimental and theoretical investigation on high-Tc superconducting intrinsic Josephson junctions

Within the last years many groups have realized and investigated different types of intrinsic Josephson junction (IJJ) arrays out of high-temperature superconducting single crystals or thin films. We tried to improve the synchronization between the junctions by external shunts. Mesa structures as well as microbridges on vicinal cut substrates showed multi-branch behaviour in their IV characteristics and random switching between branches. Theoretical modelling was done investigating phase dynamics and stability numerically as well as analytically. Branch structure in current voltage characteristics of IJJ is studied in the framework of different models, particularly, in capacitevely coupled Josephson junctions (CCJJ) model and CCJJ model with diffusion current. Results of modelling of return current in IV characteristics for stacks with different number of IJJ are presented. We discussed the possible mechanisms of synchronization and the ranges of stability. Conclusions with respect to application of such arrays such as radiation sources were given.

Suppression of Critical Current in Submicron Intrinsic Josephson Junction Fabricated in a Bi2Sr2Ca2Cu3O10+δ Single Crystal Whisker

We have fabricated intrinsic Josephson junction array stack in a Bi2Sr2Ca2Cu3O10+δ (Bi-2223) single crystal whisker using three dimensional focused ion beam milling technique. We report measurements of current density depend on junctions array at 30 K upon the junction cross-sectional area S showing a strong suppression in critical current density for junctions with S≤1 µm2. We discussed quantum fluctuations of phase in submicron junctions which is a cause for suppression of critical current density.

Dissipative Enhancement of the Supercurrent inTl2Ba2CaCu2O8Intrinsic Josephson Junctions

We have measured dissipation-induced localization of the reaction coordinate for a metastable-state decay process in a model system with moderate damping. Specifically, the supercurrent in an array of Tl2Ba2CaCu2O8 intrinsic Josephson junctions is larger when all the junctions are in the zero-voltage state than when one or more junctions are in the voltage state since the dissipation is larger in the former case.

RF-Current Effects on Intrinsic Josephson Junctions

We have fabricated intrinsic Josephson junction arrays using Tl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> thin films. The junctions have dimensions of order 1 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and therefore high slope resistance in the range 1 kOmega to 10 kOmega per junction on the quasiparticle branches. We have irradiated the junctions with microwaves at a frequency of 6.37 GHz. We observe both microwave-induced vortex-flow branches and strong suppression of the switching current but only when no junctions are in the voltage state. We attribute this observation to the shunting of the high-resistance junctions by the environmental impedance, and discuss the significance of this result for the application of intrinsic junctions as THz sources and qubits.

Spatiotemporal chaos in capacitively coupled intrinsic Josephson junction arrays and control by ashunted LCR series resonance circuit

The dynamics of capacitively coupled intrinsic Josephson junction arrays with a McCumber parameterβc<1 driven by a dc current are investigated by using numerical simulations. For the first time,spatiotemporal chaotic behaviors are found. Analysis of the dynamics of individualjunctions shows that the chaos is caused by the strong diffusive coupling between thejunctions in the array. The chaotic regions of different parameters are also presented, fromwhich the conditions for chaos are deduced. The properties of the array shunted by anLCR series resonance circuit are also investigated. The results show thatthe spatiotemporal chaos can be effectively controlled by the shuntedLCR circuit. This presents a new spatiotemporal chaos control method.

Nonlinear Inductance of Intrinsic Josephson Junction Arrays and Its Application to Tunable Filters

Nonlinear inductance of intrinsic Josephson junction arrays in Tl-2212 thin films has been investigated. Misaligned Tl-2212 thin films were fabricated on 20deg vicinal substrates and then patterned into long bridges by standard photolithography and wet chemical etching. Each bridge forms a large array of intrinsic Josephson junctions. We have measured the Josephson inductance of the bridges in the zero-DC-voltage state at 77 K and show that its dependence on the critical current is in a good agreement with theory. Also, we have numerically studied the nonlinearity of the Josephson inductance and present dependence of the distortion factor on the bias and AC signal currents. Based on the obtained results, we have designed a 10-pole narrow-band lumped-element filter with the tunable center frequency in the range from 1900 MHz to 1960 MHz. Simulations show that the filter has good selectivity.

The model of capacitively coupled intrinsic Josephson junction array and its chaotic behavior

The model of capacitively coupled intrinsic Josephson junction array was constructed with the software PSpice. Taking advantage of this new model, we investigated the behavior of capacitively coupled intrinsic Josephson junction array driven by constant current. The time domain wave, freguency spectrum, fractal dimension and phase portrait were obtained. Compared with the uncoupled array, chaotic behaviors were found firstly in the capacitively coupled intrinsic Josephson junction array. The results are valuable for the research and application of intrinsic Josephson junction arrays.

Coexistence of linear and non-linear dissipative branches in the current–voltagecharacteristics of intrinsic Josephson junction arrays

We have measured overlapping linear and non-linear branches in the hystereticcurrent–voltage characteristics of an intrinsic Josephson junction array fabricated from aTl2Ba2CaCu2O8 thin film. Analysis of the retrapping voltages and critical currents of the junctions confirmsthat the linear branches correspond to moderately-damped SIS junctions while thenon-linear branches correspond to more lightly-damped SIS junctions.

I–V Characteristic and Josephson inductance of ultra-long intrinsic Josephson junction arrays

Long intrinsic Josephson junction arrays (3.4mm) were successfully fabricated in misaligned Tl2Ba2CaCu2O8 thin films grown on 20° vicinal substrates. The array consists of about 7.7×105 intrinsic Josephson junctions. The I–V characteristic was recorded and compared with that of a 6μm long array. The inductance of the ultra-long junction array in zero-voltage state was observed and measured directly. The measured value is basically consistent with the theoretically calculated result, confirming that the inductance is mainly due to the Josephson effect. The inductance from the Josephson effect is one order of magnitude larger than that from other effects, suggesting a new idea of the use of intrinsic Josephson junction arrays as new type of inductors with small size and large inductance.

Inductance of Long Intrinsic Josephson Junction ArraysComposed of Misaligned Tl2Ba2CaCu2O8 Thin Films

We observe and measure the inductance of long intrinsic Josephsonjunction arrays composed of misalignedTl2Ba2CaCu2O8 thin films grown onLaAlO3 substrates. The array consists of about 9.1×103intrinsic Josephson junctions, where 90° phase shift between acvoltage across the array and ac current flowing through has beenmeasured. Furthermore, the voltage is proportional to the frequency ofthe current. The measured inductance values of the intrinsic Josephsonjunction arrays are basically consistent with the theoreticallycalculated results, confirming that the inductance is mainly due to theJosephson effect. The dependence of the array inductance on itscritical current is also discussed.

Josephson current suppression in three-dimensional focused-ion-beam fabricatedsub-micron intrinsic junctions

We have fabricated intrinsic Josephson junction arrays inTl2Ba2CaCu2O8 thin films using three-dimensional focused-ion-beam milling. We have measured the dependenceof the switching current density of these arrays at 4.2 K upon the junction cross-sectional area.There is strong suppression of the switching current density for junctions of area less than1 µm2, the current extrapolating to zero at an area of0.25 µm2. We discuss the possible roles of gallium ion implantation and both thermal and quantumfluctuations in this current suppression.

Exploring the Versatility of Double-Sided Fabrication of Intrinsic Josephson Junctions

After a brief description of the double-sided fabrication process, we give an example to show that a quite large array of intrinsic Josephson junctions (IJJs) can be made by superconductively connecting 256 stacks of junctions together. Each of these stacks contains only 40 junctions which prevents problems causing by heating. We present a detailed discussion on a new structure we have developed in which an extra electrode can be fabricated in the middle of an array by a slight modification of the double-sided process. Using this middle electrode, we can determine further information on the physical processes inside the stack than is possible without such an electrode. Finally we shall discuss terahertz generation in IJJs when an external magnetic field is applied perpendicular to the width of the junctions.

Fabrication of DC SQUIDs Based on&amp;lt;tex&amp;gt;$rm Bi_2rm Sr_2rm CaCu_2rm O_y$&amp;lt;/tex&amp;gt;Intrinsic Josephson Junctions

We report on the first observation of clear voltage modulation in dc SQUID based on intrinsic Josephson junctions of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/. Stacked series array of intrinsic Josephson junctions and dc SQUID based on it have been made from Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ single crystals using a double-side etching process. The number of junctions in the stack is rather controllable by monitoring the junction resistance at room temperature. The current-voltage characteristics of the SQUIDs with stacks of 20-50 IJJs at 4.2 K exhibit additional closely spaced branches together with typical multiple quasi-particle branches with voltage spacing of /spl sim/20 mV. On applying magnetic field clear periodic modulation of the lowest critical current and voltage of the SQUID are observed and the flux period obtained from the voltage-flux characteristics agrees with one flux quantum. The maximum voltage modulation and transfer function are about 80 /spl mu/V and 0.75 mV//spl Phi//sub 0/ at 26 K, respectively. The property of dc SQUID with shunt resistances is also discussed.