Mr. Jonathan Shvartzberg

Quantum effects in doubly-connected superconducting nanostructures

The present research aims at addressing a number of open questions that have arisen in previous studies of superconducting nano-rings.

Specifically, (a) The SQUID behavior of nano-loops was ascribed to inhomogeneous spatial dependence of the order parameter in loops connected to superconducting leads. Although this model relies on the theoretical work of de-Gennes and Alexander it has never been experimentally approved. We plan to confirm this theory directly by measuring the order parameter along a nano-ring using normal-metal/insulator/superconductor junctions.
 

(b) The effect of fluctuations in the order parameter on the magnetoresistance oscillations in nano-loops has not yet been studied. Recent unpublished measurements in NbN nano-rings revealed oscillations of both hc/e and hc/2e periodicities in the presence of quantum phase slips. Thought fluctuations in the order parameter are expected to destroy pair coherence, we suspect that these fluctuations allow interference of coherent quasi-particles in conduction channels, borne out in the experiment as the Aharonov-Bohm hc/e periodicity and its harmonics. In an effort to test this conjecture we plan a study of NbN rings with different rim width to control experimentally the probability of quantum phase slips, aiming to confirm the Aharonov-Bohm characteristics of the magnetoresistance oscillations.

(c) The nature of the magnetoresistance oscillations with exotic periodicities, such as 3hc/2e and hc/3e , has not been yet understood. Such exotic periodicities were also observed in our studies, in the transition region between hc/e and hc/2e. Such exotic periodicities may result from the existence of multiple Josephson junctions in the ring originating from a granular structure of the material .