Europhys. Lett.
Volume 68, Number 1, October 2004
Page(s) 86 - 92
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 September 2004
Europhys. Lett., 68 (1), pp. 86-92 (2004)
DOI: 10.1209/epl/i2004-10165-x

Half- ${h/2\ab{e}}$ critical current -Oscillations of SQUIDs

C. W. Schneider1, G. Hammerl1, G. Logvenov1, T. Kopp1, J. R. Kirtley2, P. J. Hirschfeld3 and J. Mannhart1

1  Experimentalphysik VI, Center for Electronic Correlations and Magnetism Institute of Physics, Augsburg University - D-86135 Augsburg, Germany
2  IBM Thomas J. Watson Research Center - P.O. Box 218 Yorktown Heights, NY 10598, USA
3  Department of Physics, University of Florida - Gainesville, FL 32611, USA

received 3 May 2004; accepted 29 July 2004

The current-voltage characteristics of Superconducting Quantum Interference Devices (SQUIDs) are known to modulate as a function of applied magnetic field with a period of one flux quantum $\Phi_0=h$/2e. Here we report on the fabrication and properties of SQUIDs modulating with a fundamental period of $1/2\times\Phi_0$. The characteristics of these bicrystal SQUIDs are consistent with either a strong sin(2 $\varphi$) component of the current-phase relation of the Josephson current, or with an interaction between the Cooper pairs, causing an admixture of quartets to the condensate.

74.20.Rp - Pairing symmetries (other than s-wave).
85.25.Dq - Superconducting quantum interference devices (SQUIDs).
85.25.Cp - Josephson devices.

© EDP Sciences 2004