Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 15: Superconductivity - Tunneling, Josephson Junctions, SQUIDs

TT 15.10: Talk

Tuesday, March 27, 2007, 17:00–17:15, H20

Macroscopic Quantum Tunneling of Bi₂Sr₂CaCu₂O_8+δ Intrinsic Josephson Junction SQUIDs — •X. Y. Jin, J. Lisenfeld, Y. Koval, A. V. Ustinov, and P. Müller — Physikalisches Institut III, Universität Erlangen-Nürnberg

The properties of Bi₂Sr₂CaCu₂O_8+δ superconducting rings broken by intrinsic Josephson junction stacks were studied. The stack height was between 4 and 50 junctions. SQUID behavior was observed in all devices. The modulation depth of the critical currents increased with decreasing number of junctions in the stack, and conformed to the β_L values. Crossover temperatures between the thermal and the quantum regime were in the range of 300 to 600 mK. Whereas the small stacks behaved like series arrays of independent junctions, the larger stacks were uniform and showed anomalous enhancement of escape rates. An unconventional correlated retrapping was observed, i.e., the retrapping probability decayed exponentially with the trapped flux. This phenomenon indicates that the intrinsic SQUID is a strongly driven Tera-Hertz harmonic oscillator in phase space, where intrinsic Josephson junction stacks can provide both very high inductance and very high charging energy simultaneously. Possible implications for the realization of high-T_c phase qubits are discussed.