Magneto-transport measurements in YBa2Cu3O 7-δ nanowires, comprising a single layer of a small number of grains, reveal periodic magnetoresistance oscillations in a wide temperature range below the transition. The rich structure of these oscillations manifests a negative magnetoresistance in the initial part of each cycle beginning at zero magnetic field. The salient features of these unique oscillations indicate the presence of π Josephson junctions in the granular wires, arising from the d-wave pairing symmetry in YBa2Cu3O7-δ.
Bibliographical noteFunding Information:
This work was supported partly by the OTKA grants No. T023063 and T029387 to GS, and an FWF-grant (P-12748-MOB) to CPK. Thanks are due to G. J. Samuels (Beltsville) and E. Lieckfeldt (Berlin) for sharing unpublished data).