Number Of Intrinsic Josephson Junctions Research Articles

Study of Radiation Characteristics of Intrinsic Josephson Junction Terahertz Emitters with Different Thickness of Bi2Sr2CaCu2O8+δ Crystals.

The radiation intensity from the intrinsic Josephson junction high- superconductor BiSrCaCuO terahertz emitters (Bi2212-THz emitters) is one of the most important characteristics for application uses of the device. In principle, it would be expected to be improved with increasing the number of intrinsic Josephson junctions N in the emitters. In order to further improve the device characteristics, we have developed a stand alone type of mesa structures (SAMs) of Bi2212 crystals. Here, we understood the radiation characteristics of our SAMs more deeply, after we studied the radiation characteristics from three SAMs (S1, S2, and S3) with different thicknesses. Comparing radiation characteristics of the SAMs in which the number of intrinsic Josephson junctions are N∼ 1300 (S1), 2300 (S2), and 3100 (S3), respectively, the radiation intensity, frequency as well as the characteristics of the device working bath temperature are well understood. The strongest radiation of the order of few tens of microwatt was observed from the thickest SAM of S3. We discussed this feature through the -relationship and the radiation efficiency of a patch antenna. The thinner SAM of S1 can generate higher radiation frequencies than the thicker one of S3 due to the difference of the applied voltage per junctions limited by the heat-removal performance of the device structures. The observed features in this study are worthwhile designing Bi2212-THz emitters with better emission characteristics for many applications.

Mutually Synchronized Macroscopic Josephson Oscillations Demonstrated by Polarization Analysis of Superconducting Terahertz Emitters

We demonstrate mutual synchronization of Josephson oscillations in multiple stacks of intrinsic Josephson junctions of the cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta }$. Detailed analysis of the full polarization parameters allows the determination of a phase correlation between the stacks: a simultaneous emission state is described by a linear combination of individual emission states with a phase retardation. This proves that the stacks are coupled via a Josephson plasma in a superconducting substrate and the coupling matrices can be extracted from polarization analyses. Our findings suggest a route towards the realization of high-power terahertz sources based on the synchronization of a large number of intrinsic Josephson junctions.

I – V characteristics and THz radiation properties of Bi2212 mesas

Large mesa structures composed of intrinsic Josephson junctions (IJJs) are expected to be one of a promising source of THz electromagnetic wave. In order to study the collective dynamics in large mesas with and without the influence of self-heating effect, two types of mesa structures are fabricated. One is a double-mesa structure which enables the non-uniform bias current distribution to examine the heat-flow in large mesas. We find that the current lead geometry strongly affects the collective switching of IJJs into resistive state even if the number of IJJs in the mesas is the same. Another is a standard rectangular mesa structure used in the emission experiments. In this mesa, we observe THz radiation from IJJs biased at the low bias region, where the self-heating effect is almost negligible, on inner branches of multiple I – V structures and find that all of observed intense inner-branch emissions correspond to the same cavity resonance mode.

Terahertz Radiation Power Characterization and Optimization of Stack of Intrinsic Josephson Junctions

Terahertz radiation of the stack of intrinsic Josephson junctions in the mesa structure of the layered high-Tc superconductors is analyzed and presented in this work. The dependency of the radiated power to the geometrical parameters, cavity-waveguide boundaries, and magnetic and electric bias has been investigated. This has been done by numerical calculation of the previously proposed coupled sine-Gordon equations, which characterize the electromagnetic dynamics of the stack of the intrinsic Josephson junctions. Using the obtained numerical results from these coupled equations, the effect of the design parameters such as dimensions of the mesa structure and the magnitude of the applied magnetic field and the dc current on the enhancement of the radiated power is studied. Thus, the radiated power is optimized with respect to these considered parameters. By variation of the number of layers, we also investigate the effect of the number of intrinsic Josephson junctions on the total radiated power. The results from this part are also compared with the previous analytical models.

Generation and Detection of THz Radiation Using Intrinsic Josephson Junctions

Abstract We present the generation and detection of terahertz radiation using intrinsic Josephson junctions (IJJs) in Bi2Sr2CaCu2Oy single crystals. This approach allows us to detect THz radiation from large stacks consisting of a few hundred intrinsic Josephson junctions. The lateral dimensions of the fabricated IJJ oscillator mesa range from 290×50 to 290×90 μm2 and the number of IJJs which constitute the mesas is between 100 and 450, while the small mesa with the lateral dimensions of 5 × 5 μm2 is used as the high sensitive THz detector. The largest emission is always observed when the oscillator is biased at the negative resistance region of the current-voltage characteristics. We find that the emission frequency cor–responds to the second harmonics of the in-phase cavity resonance mode. This is consistent with the emission condition of the case of thick IJJ stacks reported previously.

Radiation Power Characterization and Optimization of Stack of Intrinsic Josephson Junctions

Terahertz radiation of the stack of intrinsic Josephson junctions in the mesa structure of the layered high Tc superconductors are characterized and presented in this work. The dependency of the radiated power to the geometrical parameters, cavity-waveguide boundaries and magnetic and electric bias has been investigated. This has been done by numerical calculation of the previously proposed coupled sine-Gordon equations, which characterize the electromagnetic dynamics of the stack of the intrinsic Josephson junctions. Using the obtained numerical results from these coupled equations, the effect of the design parameters such as dimensions of the mesa structure and the magnitude of the applied magnetic field and the dc current on the enhancement of the radiated power is studied. Thus, the power is optimized with respect to these considered parameters. By variation of the number of layers, which is corresponding to the number of equations in the system of the coupled sine-Gordon equations, we also investigate the effect of the number of intrinsic Josephson junctions on the total radiated power. The results from this part are also compared with the previous analytical models.

Emission of Terahertz Waves From Stacks of Intrinsic Josephson Junctions

By patterning mesoscopic crystals of 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) into electromagnetic resonators the oscillations of a large number of intrinsic Josephson junctions can be synchronized into a macroscopic coherent state accompanied by the emission of strong continuous wave THz-radiation. The temperature dependence of the emission is governed by the interplay of self-heating in the resonator and by re-trapping of intrinsic Josephson junctions which can yield a strongly non-monotonic temperature dependence of the emission power. Furthermore, proper shaping of the resonators yields THz-sources with voltage-tunable emission frequencies.

Investigation of the breakpoint region in stacks with a finite number of intrinsic Josephson junctions

We study the breakpoint region on the outermost branch of the current-voltage characteristics of stacks with different numbers of intrinsic Josephson junctions. We show that at periodic boundary conditions the breakpoint region is absent for stacks with an even number of junctions. For stacks with an odd number of junctions and for stacks with nonperiodic boundary conditions the breakpoint current increases with the number of junctions and saturates at a value corresponding to the periodic boundary conditions. The region of saturation and the saturated value depend on the coupling between the junctions. We explain the results by the parametric resonance at the breakpoint and excitation of a longitudinal plasma wave by Josephson oscillations. A method for diagnostics of the junctions in the stack is proposed.

Single intrinsic Josephson junction with double-sided fabrication technique

We make stacks of intrinsic Josephson junctions (IJJs) embedded in the bulk of very thin (d⩽100nm) Bi2Sr2CaCu2O8+x single crystals. By precisely controlling the etching depth during the double-sided fabrication process, the stacks can be reproducibly tailor-made to be of any microscopic height (0−9nm&amp;lt;d), i.e., enclosing a specified number of IJJ (0–6), including the important case of a single junction. We discuss reproducible gaplike features in the current-voltage characteristics of the samples at high bias.

Intrinsic tunneling in cuprates and manganites

The most anisotropic high temperature superconductors like Bi 2Sr 2CaCu 2O 8 (BSCCO), as well as the recently discovered layered manganite La 1.4Sr 1.6Mn 2O 7 (LSMO) are layered metallic systems where the interlayer current transport occurs via sequential tunneling of charge carriers. As a consequence, in BSCCO adjacent CuO 2 double layers form an intrinsic Josephson tunnel junction while in LSMO tunneling of spin polarized charge carriers between adjacent MnO 2 layers leads to an intrinsic spin valve effect. We present and discuss interlayer transport experiments for both systems. To perform the experiments small sized mesa structures were patterned on top of single crystals of the above materials defining stacks of a small number of intrinsic Josephson junctions and intrinsic spin valves, respectively.

Coherent mode splitting of microwave-induced fluxons inHgI2−intercalatedBi2Sr2CaCu2O8+δsingle crystals

The microwave response of small stacks of intrinsic Josephson junctions in ${\mathrm{HgI}}_{2}\ensuremath{-}\mathrm{intercalated}$ ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystals was studied. When irradiated with a microwave of frequencies higher than the junction plasma frequency, the supercurrent branch becomes resistive and splits into multiple subbranches. The number of subbranches turns out to be identical to the number of intrinsic Josephson junctions in the mesa within the experimental error. The behavior of the subbranches fits well the predicted Josephson fluxon dynamics in a strongly coupled stack of junctions.

The c-axis gap parameter and resistivity of an individual intrinsic tunnel junction in Bi-2212 single crystals

The technology for making a specified (1–100) number of intrinsic Josephson junctions in B-2212 is reported. Measurements of the resistance during the fabrication process made it possible to avoid the in-plane contribution. The c-axis resistivity ϱ c was about 30 Ω cm at 90 K and it obeyed an exponential ϱ c ( T) ∝ exp( Λ/ T), with Λ≈43 meV, suggesting a thermally activated hopping mechanism of the c-axis transport. The c-axis gap parameter of an individual junction is about one half of that reported elsewhere and is strongly temperature dependent, suggesting proximity induced superconductivity of the intermediate BiO layers in Bi-2212.