The European Physical Journal B (EPJ B)

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Eur. Phys. J. B 37, 349-361 (2004)
DOI: 10.1140/epjb/e2004-00066-4

Fractional ac Josephson effect in p- and d-wave superconductors

H.-J. Kwon¹, K. Sengupta² and V.M. Yakovenko¹

¹ Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
² Department of Physics, Yale University, New Haven, Connecticut 06520-8120, USA

yakovenk@physics.umd.edu

(Received 24 September 2003 / Published online 2 April 2004)

Abstract
For certain orientations of Josephson junctions between two p_x-wave or two d-wave superconductors, the subgap Andreev bound states produce a $4\pi$ -periodic relation between the Josephson current I and the phase difference $\phi$ : $I\propto\sin(\phi/2)$ . Consequently, the ac Josephson current has the fractional frequency $eV/\hbar$ , where V is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (not square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs. The fractional ac Josephson effect can be observed experimentally by measuring frequency spectrum of microwave radiation from the junction. We also study junctions between singlet s-wave and triplet p_x-wave, as well as between chiral $p_x\pm ip_y$ -wave superconductors.

PACS
74.50.+r - Tunneling phenomena; point contacts, weak links, Josephson effects.
74.70.Kn - Organic superconductors.
74.72.-h - Cuprate superconductors (high- T_c and insulating parent compounds).
74.70.Pq - Ruthenates.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2004