T. Motohashi et al., Observation of the Josephson plasma reflectivity edge in the infrared region in Bi-based superconducting cuprates, PHYS REV B, 61(14), 2000, pp. R9269-R9272
The far-infrared c-axis optical reflectivity spectra of a heavily Pb-doped
Bi2212, Bi1.6Pb0.6Sr1.8CuCu2Oy, single crystal (T-c=65 K) were measured in
the superconducting state. The crystal was found to be carrier overdoped as
the optical phonons are weakly screened by the electronic excitations in t
he far-infrared region. Below T-c, a sharp reflectivity edge was observed,
corresponding to the appearance of the Josephson plasma in the superconduct
ing state. The plasma edge frequency reached 40 cm(-1) at 8 K, which is com
parable with that observed for other cuprates with much less anisotropy. Th
e c-axis penetration depth lambda(c) = 12.6 mu m was estimated from the uns
creened plasma frequency w(ps)(c)=126.2 cm(-1). This lambda(c) value is one
order of magnitude smaller than that of the optimally doped pure Bi2212, r
eflecting a drastic enhancement of the interlayer coupling in Pb-doped Bi22
12.