Shapiro step response in Bi 2Sr 2CaCu 2O 8+ δ in parallel and tilted magnetic field

Abstract

We report the first observation of Shapiro step response in the Josephson flux-flow state of Bi 2Sr 2CaCu 2O 8+ δ in strong magnetic field ( H ∥>1 T) in ab plane. Phase of external microwave radiation and internal Josephson oscillation were locked in whole stack ( N=67) of intrinsic Josephson junctions. Steps were observed at voltages V st= pNhν/2 e, with p integer, ν=45–142 GHz. As a matter of fact V st remains constant and demonstrates that the Josephson vortices move at the same speed over the whole stack of junctions keeping the high special regularity. We also observed Shapiro steps at fields tilted with respect to the c-axis. The height of Shapiro steps and Josephson critical current increase sharply with increasing tilted angle and then both decrease at larger angle. We attribute this anomaly to the interaction between Josephson and pancake vortices.