University of Maryland

Title: Andreev bound states in superconductors: Spontaneous soliton formation and fractional Josephson effect

Abstract: First [1], we show that a pi-soliton (kink) should spontaneously form in a one-dimenstional superconducting quantum wire when the total number of electron is odd. This happens because the Andreev bound states of electrons in the soliton reduce the total energy of the system. If such a wire is closed in a ring, the phase difference between the two sides of the soliton will generate a supercurrent detectable by a SQUID. The two degenerate states with the current flowing clockwise or counterclockwise can be utilized as a qubit.

Second [2], we show that the contribution of the Andreev bound states to the Josephson effect between two unconventional (p-wave organic or d-wave high-Tc) superconductors has the period of 4pi in the phase difference. Consequently, the ac Josephson current has the fractional frequency eV/h, a half of the conventional value. In the tunneling limit, the Josephson current is proportional to the first power of tunneling amplitude and is carried by single electrons, rather than Cooper pairs.

References:
[1] H.-J. Kwon, V. M. Yakovenko, PRL 89, 017002 (2002).
[2] H.-J. Kwon, K. Sengupta, V. M. Yakovenko, cond-mat/0210148.