Coherent THz emission of Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks in the hot spot regime

TL;DR

This study demonstrates coherent THz emission from Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks in the hot spot regime, showing tunability and unexpected narrow linewidths due to potential synchronization mechanisms.

Contribution

It reveals a new regime of THz emission involving hot spots and standing waves, with insights into synchronization beyond cavity resonance effects.

Findings

Coherent THz emission occurs at high power with hot spots.

Emission frequency can be tuned by hot spot size.

Linewidths are narrower than cavity quality factor predictions.

Abstract

We report on THz emission measurements and low temperature scanning laser imaging of Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the "cold" part of the stack, coexist. By varying the hot spot size the cavity resonance frequency and the emitted radiation can be tuned. The linewidth of radiation is much smaller than expected from the quality factor of the cavity mode excited. Thus, an additional mechanism of synchronization seems to play a role, possibly arising from nonequilibrium processes at the hot spot edge.