Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 67: Topological Insulators 5 (jointly with DS, HL, MA, and O)

TT 67.9: Talk

Friday, March 15, 2013, 11:45–12:00, H18

Fermion-parity anomaly of the critical supercurrent in the quantum spin-Hall effect — •Jan Dahlhaus¹, Dmitry Pikulin¹, Timo Hyart¹, Henning Schomerus², and Carlo Beenakker¹ — ¹Instituut-Lorentz, Universiteit Leiden, Niederlande — ²Department of Physics, Lancaster University, United Kingdom

The helical edge state of a quantum spin-Hall insulator can carry a supercurrent in equilibrium between two superconducting electrodes (separation L, coherence length ξ). We calculate the maximum (critical) current I_c that can flow without dissipation along a single edge, going beyond the short-junction restriction L≪ξ of earlier work, and find a dependence on the fermion parity of the ground state when L becomes larger than ξ. Fermion-parity conservation doubles the critical current in the low-temperature, long-junction limit, while for a short junction I_c is the same with or without parity constraints. This provides a phase-insensitive, dc signature of the 4π-periodic Josephson effect.