Dresden 2011 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 20: Focused Session: 50 Years of Flux Quantization
TT 20.3: Invited Talk
Tuesday, March 15, 2011, 11:40–12:10, HSZ 03
Flux Quantization driving Fractional Flux Quantum Generation — •Hans Hilgenkamp — University of Twente and Leiden University, The Netherlands
The single-valuedness of the superconducting wave function has peculiar consequences in ring structures in which phase-shifting elements are introduced. It namely demands that such phase-shifts are compensated to an integer multiple of 2π, for which the spontaneous generation of a corresponding/complementary fraction of a magnetic flux quantum by the ring is one possible option.
For example, in rings containing an element with a phase-shift of π, a spontaneous flux of a half the regular flux quantum is to be expected as the energetic ground state. This half flux quantum can have either up or down polarity, mimicking in a way the electron spin in a macroscopic structure.
This remarkable effect was key to proving the d-wave symmetry of the high-Tc superconductors, in the famous Tsuei-Kirtley tricrystal ring experiment in the early 1990’s.
By connecting high-Tc superconductors with their s-wave low-Tc counterparts it became possible to generate and couple a multitude of fractional flux quanta on a single chip. Similar developments are taking place using other forms of phase-shifters, such as Superconductor-Ferromagnet-Superconductor Josephson junctions. Besides for basic studies, such spontaneous-flux generating structures have proven to be of interest as new building blocks for superconducting (quantum)-electronics.