Local SiC photoluminescence evidence of hot spot formation and sub-THz coherent emission from a rectangular Bi2Sr2CaCu2O8+δ mesa

摘要

From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature Tc superconductor Bi2Sr2CaCu2O8+δ, the local surface temperature T(r) was directly measured during simultaneous sub-THz emission from the N∼103 intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents I and low bath temperatures Tbath≲35 K, the center of a large elliptical hot spot with T(r)>Tc jumps dramatically with little current-voltage characteristic changes. The hot spot does not alter the ubiquitous primary and secondary emission conditions: the ac-Josephson relation and the electromagnetic cavity resonance excitation, respectively. Since the most intense sub-THz emission was observed for high Tbath≳50 K in the low I bias regime where hot spots are absent, hot spots cannot provide the primary mechanisms for increasing the output power, the tunability, or promoting the synchronization of the N IJJs for the sub-THz emission, but can at best coexist nonmutualistically with the emission. No T(r) standing waves were observed.