Interaction of hot spots and THz waves in Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks of various geometry

TL;DR

This study explores how hot spots and electromagnetic standing waves interact in Bi-2212 Josephson junction stacks of different shapes, affecting THz emission and wave control.

Contribution

It demonstrates the ability to manipulate standing waves via hot spot positioning in various geometries, advancing understanding of THz emission control in superconducting devices.

Findings

Standing waves can be turned on and off by hot spot position.

Hot spots coexist with cavity resonances in superconducting regions.

Geometry influences hot spot and wave formation.

Abstract

At high enough input power in stacks of Bi_2Sr_2CaCu_2O8 intrinsic Josephson junctions a hot spot (a region heated to above the superconducting transition temperature) coexists with regions still in the superconducting state. In the ``cold'' regions cavity resonances can occur, synchronizing the ac Josephson currents and giving rise to strong coherent THz emission. We investigate the interplay of hot spots and standing electromagnetic waves by low temperature scanning laser microscopy and THz emission measurements, using stacks of various geometries. For a rectangular and a arrow-shaped structure we show that the standing wave can be turned on and off in various regions of the stack structure, depending on the hot spot position. We also report on standing wave and hot spot formation in a disk shaped mesa structure.