Statistics of avalanches in the self-organized criticality state of a Josephson junction
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AL, NONLINEAR, AND SOFT MATTER PHYSICS
Statistics of Avalanches in the SelfOrganized Criticality State of a Josephson Junction E. V. Matizen, V. G. Martynets*, and P. P. Bezverkhii Nikolaev Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences, pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia email: [email protected] Received October 30, 2009
Abstract—Magnetic flux avalanches in Josephson junctions that include superconductor–insulator–super conductor (SIS) tunnel junctions and are magnetized at temperatures lower than approximately 5 K have been studied in detail. Avalanches are of stochastic character and appear when the magnetic field penetration depth λ into a junction becomes equal to the length a of the Josephson junction with a decrease in the tem perature. The statistical properties of such avalanches are presented. The size distribution of the avalanches is a power law with a negative noninteger exponent about unity, indicating the selforganized criticality state. The selforganized criticality state is not observed in Josephson junctions with a superconductor–normal metal–superconductor (SNS) junction. DOI: 10.1134/S1063776110080261
1. INTRODUCTION In this work, we analyze the statistics of magnetic flux avalanches appearing in large regular Josephson junctions with superconductor–insulator–supercon ductor (SIS) junctions in a selforganized criticality state. Although Josephson structures have been investi gated for several decades, the magnetic response of regular Josephson junctions of various geometric shapes and various Josephson junctions is poorly stud ied experimentally. In our preceding experiments regarding the measurement of the magnetic moment of Josephson junctions [1–3] as a function of the mag netic field and temperature, we revealed three phe nomena. (i) In addition to the observed regular peaks, sharp disordered variations of the magnetic moment, which correspond to the magnetic flux avalanches whose size distribution is powerlaw, appear on magnetic hyster esis loops with a decrease in the temperature. This indicates that the Josephson junction transits to the selforganized criticality state. (ii) The selforganized criticality state appears in SIS junctions and does not appear in a junction with superconductor–normal metal–superconductor junctions (SNS junction). (iii) Regular peaks, which correspond to the pene tration of one fluxon (magnetic flux quantum) to every cell, appear on the hysteresis loops of the SNS junc tion with an increase in the magnitude of the external field. In the inverse branch of a hysteresis loop (i.e., with a decrease in the magnitude of the external field), peaks are absent and fluxons leave the junction disor
deredly; i.e., the old structure of fluxons is apparently fused. The first phenomenon was theoretically explained in [4, 5]. Unfortunately, the physical meaning of the second and third phenomena is still unclear. In this work, we report new measurements of the magnetic moment of the triangle SIS junction
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