Probing the collective Josephson plasma resonance in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+y}$ by $W$-band-mixing experiments

We report on $W$-band-mixing experiments with mesa structures patterned on top of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+y}$ single crystals. Due to the intrinsic Josephson effect the mixing process could be observed. There is a steep increase of the mixing intensity when the bias current approaches the critical current. We show that the mixing response is related to the excitation of the collective Josephson plasma resonance. In magnetic fields we observed a decrease of the Josephson plasma frequency. From this dependence we were able to estimate the frequency of the Josephson plasma resonance for zero bias and zero field ranging from 105 to 220 GHz.