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IEEE Transactions on Applied Superconductivity

The observation of subharmonic peculiarities of I-V characteristic of edge-type Josephson junction chains placed in microwave resonator

Andrey P. Lipatov, V.A. Ilyin, A. Verevkin

Published Jun 1, 1997• 0 citations
Publisher

Abstract

The spectrums of own Josephson radiation and I-V characteristics of one-dimensional chains of edge-type Nb Josephson junction placed into microwave resonator have been studied. The interaction with the external resonator caused synchronization of junctions forming the chain. This effect was detected experimentally. In the hysteresis region of I-V characteristic we have found the presence of own radiation area. Its bounds are determined by the value of junction characteristic voltage and are practically independent from the value of chain bias voltage. The studies of negative differential resistance region of I-V characteristic shows the presence of thin structure which may be interpreted as a set of subharmonic steps caused by the coupling of Josephson junction own radiation with external microwave resonator.

DOI
10.1109/77.621993

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The spectrums of own Josephson radiation and I-V characteristics of one-dimensional chains of edge-type Nb Josephson junction placed into microwave resonator have been studied. The interaction with the external resonator caused synchronization of junctions forming the chain. This effect was detected experimentally. In the hysteresis region of I-V characteristic we have found the presence of own radiation area. Its bounds are determined by the value of junction characteristic voltage and are practically independent from the value of chain bias voltage. The studies of negative differential resistance region of I-V characteristic shows the presence of thin structure which may be interpreted as a set of subharmonic steps caused by the coupling of Josephson junction own radiation with external microwave resonator.
We have been investigated the current - voltage characteristics of naturally stacked intrinsic Josephson junctions in mesa-shaped single crystals, having dimensions in the ab plane larger than the Josephson penetration depth, without and with microwave irradiations. In the absence of microwave irradiation, a gaplike feature and multiple resistive branches that imply SIS series junctions were observed in the current - voltage characteristic. Under appropriate conditions of microwave irradiation, we successfully observed striking microwave-induced subharmonic steps, caused by the phase-locked oscillation of a coupled multifluxon, with nearly equal voltage separations on the I - V characteristics of a mesa in the cavity resonant mode.
Abstract Parametric amplification of a high-frequency radiation by point-like Josephson junctions in the cavity has been studied within a resistive model. It is shown numerically and analytically that near the subharmonic steps of the current–voltage characteristic there are areas of amplification of electromagnetic radiation. An one-dimensional array of the Josephson point junctions connected in series is treated. It is shown that the junctions in the array near the subharmonic steps of current–voltage characteristic are nonsynchronized and, accordingly, the amplification regions near the subharmonic steps of the array are missing.
Josephson soliton oscillators integrated in a resonator consisting of two closely spaced coplanar superconducting microstrips have been investigated experimentally. Pairs of long 1-D Josephson junctions with a current density of about 1000 A/cm/sup 2/ were made using the Nb-AlO/sub x/-Nb trilayer technique. Different modes of half-wave resonances in the thin-film structure impose different magnetic field configurations at the boundaries of the junctions. The DC I-V characteristic shows zero-field steps with a number of resonator-induced steps. These structures are compared to RF-induced steps generated by phase-locking of the soliton motion to an external microwave source. The two different resonant configurations identified may be interpreted as a coupling to the microwave field at the end boundary and as a more homogeneous coupling distributed over the junction length.>
An experimental investigation is made of the subharmonic Shapiro steps observed on the I-V curves of high-T c superconductor Josephson junctions and on the bias-voltage dependences of the rf noise and detector response when the junctions are subjected to external submillimeter radiation. Structures of this type are ordinarily described by a nonsinusoidal current-phase relation, which is why subharmonic steps appear. Numerical modeling of the processes occurring in a Josephson junction by means of a simple current-phase relation, as in the case of an SNS junction, gives good agreement with experiment. The width of the characteristic Josephson generation line of the junction was estimated on the basis of the noise dependences and the selective detector response. The width can be explained by taking into account the shot noise of the tunneling component of the conductivity. A model of the conductivity of a high-T c superconductor Josephson junction, consisting of a tunnel junction with microshorts possessing metallic conductivity, is discussed.
We report an experimental and theoretical study of low-voltage resistive states observed in small tunnel Josephson junctions subject to microwave radiation. The observed features result from Shapiro steps in the current–voltage characteristics and appear when both thermal fluctuations and high frequency dissipation are strong. Without microwave radiation, Josephson junctions have a phase diffusion supercurrent branch characterized by a finite small resistance and hysteretic switching to a higher voltage range under these conditions. When microwave radiation is applied, three different types of resistive states are observed in the current-voltage characteristics. First, a phase diffusion branch steadily evolves and its maximum voltage Vm increases with the microwave power. Another interesting observed feature is a zero-crossing resistive state characterized by a negative resistance. Finally, we find that the low-voltage resistive state can split into numerous hysteretic fine branches resembling incoherent Shapiro-like steps. The appearance of a particular resistive state depends on the interrelations among the Josephson energy EJ, the energy kBT of thermal fluctuations, and the microwave frequency ω. A theoretical analysis based on incoherent multi-photon absorption by a junction biased in the Josephson phase diffusion regime is in good agreement with the experimental observations.
The subharmonic gap structure (SGS) in long-overlap Nb-AlOx-Nb Josephson tunnel junctions has been investigated. The experimental results show peaks in the differential conductance at both odd and even integer fractions of the gap voltage, VG. Furthermore, the conductance peaks at VG/2 has been observed to split into two peaks with different characteristics. At high magnetic fields, the I-V characteristics approach a single curve, while retaining the SGS conductance peaks. The gap structure and the SGS show the same temperature dependence. The SGS can be explained by a Josephson self-coupling effect or multiple Andreev reflections. The results are important for the development of the flux flow oscillator used a local oscillator in integrated all-superconducting 200-800 GHz receivers.