2003/01/31 by Michio Watanabe, David B. Haviland
Physics and Astronomy · #cond-mat.mes-hall #cond-mat.dis-nn
paper · pdf · doi:10.1103/physrevb.67.094505
published as Phys. Rev. B vol. 67, 094505 (2003) · 11 pages with 14 embedded figures, RevTeX4, final version
arxiv created 2003/03/19 · arxiv updated 2009/11/30
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 R0' of the SQUID arrays is much higher than the quantum resistance RK = h/e2 = 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 R0' >> RK. The numerical calculation agrees with the experiments qualitatively. We also discuss the R0' dependence of the single-Josephson-junction I-V curve in terms of the superconductor-insulator transition driven by changing the coupling to the environment.