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IEEE Transactions on Applied Superconductivity

FIR response of intrinsic Josephson junctions

S. Rother, Yuri Koval, Paul Müller, R. Kleiner, Yuji Kasai, Kensuke Nakajima, Marian Darula

Published Mar 1, 2001• 12 citations
Publisher

Abstract

We present experiments on the far infrared response of intrinsic Josephson junctions in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO). We detected first order Shapiro steps on resistive branches in a frequency range between 584 GHz and 2.5 THz. Due to the very low power coupled into the junctions the suppression of the critical current was only weak. With increasing number of junctions in the resistive state a higher amplitude of the Shapiro steps was measured. As the frequencies are well above the plasma frequency of our junctions, the steps are expected to be stable at any power level. To verify this, step heights were studied at various power levels as a function of frequency. The impedance matching of the system improved considerably when several junctions have switched into the resistive state.

DOI
10.1109/77.919562

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IEEE Transactions on Applied Superconductivity•Jun 1, 2009•1 citation
We present experiments on the far infrared response of intrinsic Josephson junctions in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ (BSCCO). We detected first order Shapiro steps on resistive branches in a frequency range between 584 GHz and 2.5 THz. Due to the very low power coupled into the junctions the suppression of the critical current was only weak. With increasing number of junctions in the resistive state a higher amplitude of the Shapiro steps was measured. As the frequencies are well above the plasma frequency of our junctions, the steps are expected to be stable at any power level. To verify this, step heights were studied at various power levels as a function of frequency. The impedance matching of the system improved considerably when several junctions have switched into the resistive state.
We have investigated the RF-induced steps in intrinsic Josephson junctions in mesa-shaped Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ single crystals. By applying RF signal in the frequency range 2-20 GHz to the mesa, two types of responses were observed depending on the frequency of the applied microwave. One is the Shapiro step response observed at the frequencies above the Josephson plasma frequency for surface junction. Another is the microwave-induced vortex flow response for surface and inner junctions. We found that the junction size is also the key condition for the observation of Shapiro steps together with the frequency of applied microwave.
We have studied the far infrared behavior of high -T/sub c/ superconductor-normal metal-superconductor (SNS) microbridges with T/sub c/>85 K and critical current-resistance products (I/sub c/R/sub N/) as high as 10 mV at 4 K. These are the highest I/sub c/R/sub N/ products reported to date for microfabricated Josephson junctions of any material. The junctions were integrated at the feeds of planar log-periodic antennas made from Au thin films. The junctions had dc normal state resistances R/sub N/ between 6 and 38 /spl Omega/, reasonably well matched to the antenna's estimated RF impedance of 53 /spl Omega/. Far infrared laser radiation at 404, 760, and 992 GHz induced distinct Shapiro steps (i.e. constant voltage steps at voltages n(hf/2e), n=1,2,...) in the current voltage characteristics as well as modulation of the critical current. Steps were observed at voltages up to 17 mV and 6 mV, at temperatures of 9 K and 57 K respectively. This corresponds to maximum Josephson oscillation frequencies of 8 and 3 THz at these temperatures. These are the first far infrared measurements performed on high T/sub c/ junctions. Measurements of the power, frequency, and temperature dependence of the Shapiro steps are presented and discussed in the context of a resistively and capacitively shunted junction (RCSJ) model. A value of 4.5 fF for the junction capacitance is inferred from the hysteresis of the slightly underdamped current-voltage characteristics.>
We have studied the far infrared behavior of high -T/sub c/ superconductor-normal metal-superconductor (SNS) microbridges with T/sub c/>85 K and critical current-resistance products (I/sub c/R/sub N/) as high as 10 mV at 4 K. These are the highest I/sub c/R/sub N/ products reported to date for microfabricated Josephson junctions of any material. The junctions were integrated at the feeds of planar log-periodic antennas made from Au thin films. The junctions had dc normal state resistances R/sub N/ between 6 and 38 /spl Omega/, reasonably well matched to the antenna's estimated RF impedance of 53 /spl Omega/. Far infrared laser radiation at 404, 760, and 992 GHz induced distinct Shapiro steps (i.e. constant voltage steps at voltages n(hf/2e), n=1,2,...) in the current voltage characteristics as well as modulation of the critical current. Steps were observed at voltages up to 17 mV and 6 mV, at temperatures of 9 K and 57 K respectively. This corresponds to maximum Josephson oscillation frequencies of 8 and 3 THz at these temperatures. These are the first far infrared measurements performed on high T/sub c/ junctions. Measurements of the power, frequency, and temperature dependence of the Shapiro steps are presented and discussed in the context of a resistively and capacitively shunted junction (RCSJ) model. A value of 4.5 fF for the junction capacitance is inferred from the hysteresis of the slightly underdamped current-voltage characteristics. >
The microwave response properties of Bi 2 Sr 2 CaCu 2 O 8+x long intrinsic Josephson junctions have been experimentally and theoretically investigated. We fabricated a mesa structure consisting of 14 junctions, 50 μm long and 4 μm wide, and observed the microwave-induced steps in the I-V characteristics under irradiation with microwaves in the range 5–8 GHz. The step voltages were proportional to the square root of the microwave power, implying that the steps were produced by the motion of fluxons created by the microwaves. The Josephson frequency corresponding to the maximum step voltage was estimated to be 570 GHz. The step voltage decreased with increasing temperature, which can be explained by the decrease of the Swihart velocity. We performed a numerical simulation using coupled sine-Gordon equations and obtained a power dependence of the step voltage similar to the experimental result, and demonstrated standing waves of electric fields with in-phase plasma oscillation in all the junctions. These facts suggest that the steps observed in the experiment were produced by plasma resonance excited by the external microwaves.
The high-frequency response of bicrystal YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Josephson junctions for far infrared laser irradiation is presented. The junctions on silicon and MgO substrates exhibit a remarkable first order Shapiro step for the methanol line at 1.76 THz. dV/dI measurements reveal several steps corresponding to the methanol lines at 1.48, 1.76 and 2.53 THz. The line width of Josephson oscillation at these frequencies is estimated from the width of the Shapiro steps. It is suggested that the excess shot noise broadens the line width.
We have fabricated intrinsic Josephson junction arrays using Tl2Ba2CaCu2O8thin films. The junctions have dimensions of order 1 mum2and 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.