Magnetic flux periodicity of h/e in superconducting loops

Abstract

Superconducting loops exhibit macroscopic quantum phenomena that have far-reaching implications; magnetic flux periodicity and flux quantization are the key to our understanding of fundamental properties of superconductors and are the basis for many applications. In superconducting rings, the electrical current responds to a magnetic flux by having a periodicity of h/2e, where the ratio of Planck’s constant and the elementary charge defines the magnetic flux quantum h/e. The well-known h/2e periodicity is a hallmark for electronic pairing in superconductors and is considered evidence for the existence of Cooper pairs. Here, we show that in contrast to this long-held belief, rings of many superconductors bear an h/e periodicity. These superconductors include the high-temperature superconductors, Sr2RuO4, the heavy-fermion superconductors, as well as all other unconventional superconductors with nodes (zeros) in the energy gap, and conventional s-wave superconductors with small gaps. As we show, the 50-year-old Bardeen–Cooper–Schrieffer theory of superconductivity implies that for loops of such superconductors the ground-state energies and consequently also the supercurrents are generically h/e periodic.

Cite this article

Loder, F., Kampf, A., Kopp, T. et al. Magnetic flux periodicity of h/e in superconducting loops. Nature Phys 4, 112–115 (2008). https://doi.org/10.1038/nphys813

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