Direct imaging of hot spots in Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} mesa terahertz sources

TL;DR

This study uses fluorescence imaging to directly visualize hot spots in Bi-2212 superconducting stacks, revealing non-uniform temperature distributions that exceed the superconducting transition during terahertz emission.

Contribution

It provides the first direct imaging evidence of hot spots in Bi-2212 stacks during THz emission, linking hot spot formation to emission conditions.

Findings

Hot spots can form in Bi-2212 stacks during THz emission.

Temperature in the middle of the stack can exceed the superconducting transition.

Non-uniform temperature distribution is directly observed.

Abstract

Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} (Bi-2212) are a promising source of coherent continuous-wave terahertz radiation. It is thought that at electrical bias conditions under which THz-emission occurs hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power. Here we perform an imaging study of the temperature distribution at the surface of BSCCO stacks utilizing the temperature-dependent 612nm fluorescence line of Eu^{3+} in a europium chelate. The images directly reveal a highly non-uniform temperature distribution in which the temperature in the middle of the stack can exceed the superconducting transition temperature by tens of Kelvin under biasing conditions typical for THz-emission.