Local SiC photoluminescence evidence of hot spot formation and sub-THz coherent emission from a rectangularBi2Sr2CaCu2O8+δmesa

Abstract

From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature ${T}_{c}$ superconductor ${\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}$, the local surface temperature $T(\mathbit{r})$ was directly measured during simultaneous sub-THz emission from the $N\ensuremath{\sim}{10}^{3}$ intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents $I$ and low bath temperatures ${T}_{\mathrm{bath}}\ensuremath{\lesssim}35$ K, the center of a large elliptical hot spot with $T(\mathbit{r})>{T}_{c}$ 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 ${T}_{\mathrm{bath}}\ensuremath{\gtrsim}50$ 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 $T(\mathbit{r})$ standing waves were observed.