c-axis superfluid response and quasiparticle conductivity in Bi2Sr2CaCu2O8+δ and Bi2Sr2CuO6+δ

Josephson plasma resonance for underdoped Bi2Sr2CaCu2O8+δ and Bi2Sr2CuO6δhave been measured by sweeping the microwave frequency continuously. The resonance enables one to determine the superfluid density and quasiparticle conductivity in the c-axis accurately. They show that the superfluid response and the low energy excitations of the condensate in the c-axis of these materials are very different from those in the ordinary Josephson multilayer tunnel junctions. The Josephson coupling energy in single layer Bi2Sr2CuO6+δis more than 5,000 times smaller than is predicted in interlayer tunneling model