Conductivity and paraconductivity in (Bi,Pb${)}_2$${\mathrm{Sr}}_2$${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{\mathit{x}}$ whiskers

We have measured the resistivity of (Bi,Pb${)}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$ ${\mathrm{Cu}}_{\mathit{n}}$ ${\mathrm{O}}_{\mathit{x}}$ single-crystal whiskers in the a and c directions. Our results indicate that the whiskers may be either 2:2:1:2 (n=1) or 2:2:2:3 (n=2) or have both phases present. Well above ${\mathit{T}}_{\mathit{c}}$, the resistivity in the a direction decreases linearly with temperature. We also studied the paraconductivity due to thermal fluctuations above ${\mathit{T}}_{\mathit{c}}$. The paraconductivity in the a direction shows quasi-one-dimensional behavior for temperatures close to ${\mathit{T}}_{\mathit{c}}$. This quasi-one-dimensional behavior may be due to a percolative conduction path. For the c direction, the resistivity is best fit by ${\mathrm{\rho }}_{\mathit{c}}$=${\mathit{Ae}}_{\mathit{g}}^{\mathrm{-}\mathit{E}}$/kT, where T is the temperature. However, as T approaches ${\mathit{T}}_{\mathit{c}}$ from above, ${\mathrm{\rho }}_{\mathit{c}}$ increases much faster than a thermally activated law, perhaps because of the fluctuations.