Current Filamentation in Large Bi 2 Sr 2 CaCu 2 O 8 + δ Mesa Devices Observed via Luminescent and Scanning Laser Thermal Microscopy

Stacked intrinsic Josephson junctions in the well studied superconductor Bi${}_{2}$Sr${}_{2}$CaCu${}_{2}$O${}_{8}$ are promising as a compact source of coherent terahertz radiation, which would have applications ranging from bioimaging to security screening. Understanding localized heating in such stacks is essential to optimizing their performance, and to this end the authors directly image the complex self-heating behaviors of these devices under bias conditions typical for THz emission. For good heat removal, narrow (compared to device size) filaments of current nucleate hot spots in asymmetric locations, which is consistent with theoretical predictions and suggests a means to enhance emission power.