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Condensed Matter Physics Seminar

2 p.m., Thursday, February 27, 2003

Room 1201, Physics Building
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* Andreev bound states in superconductors: Spontaneous soliton formation and
fractional Josephson effect*

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Victor Yakovenko

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(University of Maryland)

**Abstract:** First [1], we demonstrate that a pi-soliton (kink) should
spontaneously form in a 1D superconducting wire when the total number of
electron is odd, because Andreev bound states in the soliton would decrease 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 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 Q1D p_{x}-wave or two Q2D d-wave superconductors has the
period of 4p 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, thus the critical
current is greatly enhanced and has an unusual temperature dependence.
References:

[1] H.-J. Kwon and V. M. Yakovenko, Phys. Rev. Lett. **89**, 017002 (2002).

[2] H.-J. Kwon, K. Sengupta, and V. M. Yakovenko, cond-mat/0210148.

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