Graduate School in Nonlinear Science

Sponsored by The Danish Research Agency

MIDIT                              OFD                          CATS
Modelling, Nonlinear Dynamics      Optics and Fluid Dynamics    Chaos and Turbulence Studies
and Irreversible Thermodynamics    Risø National Laboratory     Niels Bohr Institute and 
Technical University of Denmark    Building 128                 Department of Chemistry
Building 321                       P.O. Box 49                  University of Copenhagen 
DK-2800 Lyngby                     DK-4000 Roskilde             DK-2100 Copenhagen Ø
Denmark                            Denmark                      Denmark


V.V. Ryazanov
Institute of Solid State Physics,
Russian Academy of Science,
Chernogolovka, Moscow district, 142432,

Thursday, August 23, 2001, 14:00 h
at IMM, Bldg. 305, Room 018, DTU

Abstract: It was found in [1] that the thin-film Nb-Cu1-xNi-Nb sandwiches (Josephson SFS junctions) at definite values of Ni concentrations close to 50% and at specific values of the ferromagnet layer thickness reveal the crossover to the Josephson pi-state with different signs of the superconducting order parameter at the two banks of the junction. This effect is related to a special feature of superconducting pair flow through a ferromagnet (spatial oscillations of the order parameter in presence of the exchange field). These sandwiches showed the reentrant oscillating temperature dependence of the critical current with vanishing amplitude at T=Tcr. Recently we have observed that the crossover to the pi-state also manifested itself in the half-period shift of the magnetic field dependence of the critical current in the triangular SFS arrays. The shift is associated with the appearance of spontaneous supercurrents in the array even in case of zero field, with the ground state degenerated with respect to the two possible current flow directions.

`Self-frustrated' superconducting networks with pi-junctions may be used for the realization of the superconducting quantum bit. Originally, the suggested superconducting `phase' qubits were based on magnetic-frustrated superconducting networks [2]. This system is not isolated from environment and is estimated to have shorter coherence time with respect to qubits using a pi-junction [3]. Another possible application of pi-junctions are related to the development of superconducting `complementary' electronics [4] based on the analogy to complementary metal-oxide-semiconductor (CMOS) logic family.

[1] V.V.Ryazanov, V.A.Oboznov, A.Yu.Rusanov et al., Phys. Rev. Lett. 86, 2427 (2001).
[2] J.E. Mooij et al., Science 285 (1999).
[3] G. Blatter et al. Cond-mat/9912163 (1999).
[4] E.Terzioglu, M.R. Beasley, IEEE Trans. Appl. Superc. 8 (1998) 48.