A SEM image of a double network aluminum sample.

Little and Parks showed with their experiments that the transition temperature of a superconducting cylinder oscillates in an external magnetic field with a period of Φ = h/2e [1]. Theoretical studies have found that there should be a h/e periodicity in ring-shaped or networked nano-ring unconventional superconductors that can arise via various mechanisms when the ring diameter becomes smaller than the zero-temperature coherence length, ξ0. Three proposed mechanisms that might give rise to h/e periodicity include the Aharonov-Bohm effect [2], a mechanism based on the dependence of the Cooper pair's internal energy on its motion [3], or finally via the formation of quasi-particles [4]. There is even speculation that this periodicity should be seen in rings made out of aluminum, a conventional superconductor, with diameters smaller than the coherence length [5].


A magnetoresistance measurements on a double network of aluminum.

Carillo et al. investigated this proposed periodicity in a single YBCO loop [6], Gammel et al. investigated simple networks of YBCO [7], and Sochnikov et al. began investigating this proposed periodicity in double network patterns of LSCO [8]. None of the investigations found the sought after periodicity and the amplitude of the observed oscillations was much larger than one would expect from the Little-Parks effect. Sochnikov et al. propose that this enhanced amplitude is due to interaction between thermally excited moving vortices and the oscillating persistent currents in the loops. Based on their experiments on a niobium ladder, Berdiyorov et al. propose that the enhanced amplitude is rather due to interaction between the applied current and the Meissner currents in the superconductor [9].

The aim of this project is to perform the first experiments looking for h/e-periodicity in various geometries of elemental superconductors. This data will help answer the question whether this behavior is or is not unique to high-Tc superconductors, thereby adding another important piece to the puzzle of the mechanism of high-Tc superconductivity. This project is performed in collaboration with the Institute for Superconductivity at Bar-Ilan University in Israel.

  1. W. A. Little and R. D. Parks. Phys. Rev. Lett. 9, 9 (1962)
  2. T.-C. Wei and P. M. Goldbart Phys. Rev. B 77, 224512 (2008)
  3. V. Vakaryuk Phys. Rev. Lett. 101, 167002 (2008)
  4. F. Loder et al. New J. Phys. 11, 075005 (2009)
  5. F. Loder et al. Phys. Rev. B 78, 174526 (2008)
  6. F. Carillo et al. Phys. Rev. B 81, 054505 (2010)
  7. P.L. Gammel et al. Phys. Rev. B 41, 2593 (1990)
  8. I. Sochnikov et al. Nature Nanotechnology 5, 516–519 (2010)
  9. G.R. Berdiyorov et al. Phys. Rev. 86, 224504 (2012)

Publications

  1. Flux-periodicity crossover from h/2e to h/e in aluminium nano-loops;   C. Espy1, O. J. Sharon2, J. Braun1, R. Garreis1, F. Strigl1, A. Shaulov2, P. Leiderer1, E. Scheer1,*, Y. Yeshurun2; 1Department of Physics, University of Konstanz, 78457 Konstanz, Germany,  2Department of Physics and Institute of Nano Technology and Advanced Materials, Submitted to Journal of Physics, Jun 2017
  2. R. Garreis, Magnetotransport measurements in aluminium nano loop arrays (2018)

Information

Contributors: R. Garreis, J. Braun
Former contributors: F. Strigl, C. Espy, J. Braun
External cooperations: Institute for Superconductivity at Bar-Ilan University in Israel
Period: since 2015