<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">c</mml:mi></mml:math>-Axis Superfluid Response and Quasiparticle Damping of Underdoped Bi:2212 and Bi:2201

Abstract

By sweeping the microwave frequency, we measured the Josephson plasma resonance for underdoped Bi:2212 and Bi:2201. The resonance enables us to determine the superfluid density and quasiparticle conductivity ${\ensuremath{\sigma}}_{c}^{\mathrm{qp}}$ in the $c$ axis accurately. In the slightly underdoped crystals, superfluid density shows very little change at low temperature, which is consistent with a $d$-wave coherent tunneling model. The $c$-axis superfluid response shows an unusual doping dependence. The $T$ dependence of ${\ensuremath{\sigma}}_{c}^{\mathrm{qp}}$ is very different from that in the $\mathrm{ab}$ plane. The Josephson coupling energy in single-layer Bi:2201 is a factor of 5000 smaller than predicted by the interlayer tunneling model.