Thermal Management in Large Bi2212 Mesas Used for Terahertz Sources

We present a thermal analysis of a patterned mesa on a Bi ₂ Sr ₂ CaCu ₂ O ₈ (Bi2212) single crystal that is based on tunneling characteristics of the c-axis stack of ~800 intrinsic Josephson junctions in the mesa. Despite the large mesa volume (e.g., 40 x 300 x 1.2 μm ³ ) and power dissipation that result in self-heating and backbending of the current-voltage curve (I-V), there are accessible bias conditions for which significant polarized THz-wave emission can be observed. We estimate the mesa temperature by equating the quasiparticle resistance, R _qp (T), to the ratio V/I over the entire I-V including the backbending region. These temperatures are used to predict the unpolarized black-body radiation reaching our bolometer and there is substantial agreement over the entire I-V. As such, backbending results from the particular R _qp (T) for Bi2212, as first discussed by Fenton, rather than a significant suppression of the energy gap. This model also correctly predicts the observed disappearance of backbending above ~60 K.