Microwave distribution in stacked Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+x}$ intrinsic Josephson junctions in a transmission-line geometry

The microwave distribution inside a rectangular stack (15 $\mu$m$\times$0.72 $\mu$m$\times$60 nm) of Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+x}$ intrinsic Josephson junctions (IJJs) was studied. The stack was microfabricated into a transmission-line geometry, with a few hundred nm thick Au layers deposited on top and bottom of the stack. The microwave distribution was monitored by measuring the anomalous suppression of the tunneling critical current of the IJJs with varied microwave power at frequencies in the W band. This technique can provide valuable information on the microwave transmission modes inside the sandwiched stack of IJJs, which is utterly important for the high-frequency device applications using IJJs, such as fluxon-flow THz oscillators.