Current Filamentation in Large Bi2Sr2CaCu2O8+delta Mesa Devices Observed via Luminescent and Scanning Laser Thermal Microscopy

We study the self-heating of a large stack of Bi2Sr2CaCu2O8+delta intrinsic Josephson junctions, of a configuration designed for terahertz generation. We find good qualitative agreement between direct thermoluminescent measurements of the device surface temperature and low-temperature scanning laser microscopy images. In particular, the two techniques both reveal a mode of thermal instability through the asymmetric nucleation of a small hot spot near a corner or edge of the sample. This behavior conforms with a theoretical stability analysis, and the radius of the hot spot is in excellent agreement with theoretical predictions, as is its growth with increasing bias current and bath temperature. Narrow hot spots may offer a possible means of enhancing the terahertz emission power from this type of device.