On Bose-Einstein Topological Condensation in Josephson Junctions Graph Arrays

by Matteo Cirillo (Physics Department and MINAS Lab Università di Roma "Tor Vergata" Roma, Italy)

Tuesday 8 Nov 2016, 16:00 → 18:00 Europe/Rome

Aula Conversi (Dipartimento di Fisica - ed. G.Marconi)

Bose-Einstein Condensation (BEC) has attracted renewed, and relevant, interest in the past two decades due to the evidence of the phenomenon in quantum optics. Topological issues have also led to substantial efforts in condensed matter and statistical mechanics. Theoretical predictions exist that in graph-shaped arrays of bosonic island connected by an adequate potential a Bose-Einstein "topological" condensation could take place. The BEC in this case is predicted to occur along specific branches of the graphs and is uniquely due to the connectivity of the graph itself. We will present experimental results obtained on planar patterns of superconductive islands (the bosons in this case are Cooper pairs of electrons) connected by Josephson junctions. We have observed excess, or defect, of Josephson currents along the graph directions as predicted by the model and the temperature dependence of the anomalous currents indicates that a further condensation phenomenon, below the BCS temperature, might indeed give birth to the observed phenomenon.