YBCO-Constriction Hot Spot Modeling: DC and RF Descriptions for HEB THz Mixer Noise Temperature and Conversion Gain

To investigate the THz mixing performance of YBCO hot electron bolometers (HEB), the influence of the local oscillator (LO) radiofrequency (RF) radiation has been considered in detail. As opposed to the usual hot spot modeling approach, where the LO power is assumed to be uniformly distributed over the HEB constriction length, a uniform RF current has been assumed. The local electron temperature-as obtained by solving the coupled electron and phonon thermal reservoir equations-could then be used to determine the local YBCO complex resistivity, hence the locally dissipated LO power. Besides, the use of a modified two-fluid description allowed to determine the RF-dependent temperature shift (~-1% THz^-1) and broadening (~+20% THz^-1) of the resistive transition. Finally, the impedance matching to the THz antenna was considered. For a typical constriction, the conversion loss and noise temperature T_DSB were computed, with T_DSB × exp(0.32f) behavior up to 2.5 THz.