Spontaneous frequency shift and phase delay of coupled terahertz radiations mediated by the Josephson plasmon in a cuprate superconductor

TL;DR

This study investigates how Josephson plasmon-mediated coupling causes spontaneous frequency shifts and phase delays in synchronized terahertz emissions from coupled cuprate superconductor mesas, revealing polarization-dependent interactions.

Contribution

It uncovers the role of Josephson plasmon in mediating coupling and phase delay, advancing understanding of terahertz synchronization in superconductor devices.

Findings

Coupled mesas exhibit synchronized terahertz radiation with phase delay.

Coupling mediated by Josephson plasmon causes frequency shifts.

Polarization analysis reveals coupling matrix components.

Abstract

We examine coupling interactions used to synchronize macroscopic Josephson oscillations induced in intrinsic Josephson junction (IJJ) mesa stacks made of a Bi2212 single crystal. Synchronized radiations of terahertz electromagnetic (EM) waves are detected under common voltage and current bias operations of two connected mesas with close individual radiation frequencies, while uncoupled and bimodal radiations are frequently observed in two mesas with different individual radiation frequencies. Detailed observations of the polarizations of the EM waves emitted when two mesas are biased in parallel or series allow us to reveal the coupling matrix components, which include ratios of synchronized IJJs in the mesas and phase delay between the macroscopic Josephson oscillations. A frequency evolution of the phase delay implies that the coupling between the Josephson oscillations is mediated by the small amplitude Josephson plasmon inside the superconducting substrate. This finding stimulates systematic survey on polarization of EM wave emitted from synchronized multiple mesa devices in order to realize powerful terahertz emissions from superconductors.