Quantum Effects in Small-Capacitance Single Josephson Junctions

Abstract

We have measured the current-voltage (I-V) characteristics of small-capacitance single Josephson junctions at low temperatures (T=0.02-0.6 K), where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc SQUIDs. The single-junction I-V curve is sensitive to the impedance of the environment, which can be tuned IN SITU. We have observed Coulomb blockade of Cooper-pair tunneling and even a region of negative differential resistance, when the zero-bias resistance R_0' of the SQUID arrays is much higher than the quantum resistance R_K = h/e^2 = 26 kohm. The negative differential resistance is evidence of coherent single-Cooper-pair tunneling within the theory of current-biased single Josephson junctions. Based on the theory, we have calculated the I-V curves numerically in order to compare with the experimental ones at R_0' >> R_K. The numerical calculation agrees with the experiments qualitatively. We also discuss the R_0' dependence of the single-Josephson-junction I-V curve in terms of the superconductor-insulator transition driven by changing the coupling to the environment.

11 pages with 14 embedded figures, RevTeX4, final version

References in corpus (4)

• Coulomb Blockade and Coherent Single-Cooper-Pair Tunneling in Single Josephson Junctions
• Effect of zero point phase fluctuations on Josephson tunneling
• Magetoresistance of RuO_2-based resistance thermometers below 0.3 K
• Theory of superconductor-insulator transition in single Josephson junctions

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