Superconducting fluctuations in Bi2Sr2Ca2Cu3Ox thin films: Paraconductivity, excess Hall effect, and magnetoconductivity.

Abstract

A detailed study of normal-state magnetotransport properties in (Bi,Pb${)}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$ thin films with a zero-resistance critical temperature ${\mathit{T}}_{\mathit{c}0}$=105 K prepared by dc-magnetron sputtering on MgO substrates is reported. Measurements of the electrical resistivity, the magnetoresistance, and the Hall effect are analyzed with regard to contributions of the superconducting order-parameter thermodynamic fluctuations, using theories for two-dimensional, layered superconductors. We have obtained a consistent set of parameters, i.e., the in-plane coherence length ${\ensuremath{\xi}}_{\mathit{a}\mathit{b}}$(0)=1.6 nm, the out-of-plane coherence length ${\ensuremath{\xi}}_{\mathit{c}}$(0)=0.14 nm, and the electron-hole asymmetry parameter \ensuremath{\beta}=-0.38. At temperatures below 118 K, we observe a remarkable enhancement (above theoretical predictions) of both the excess Hall effect and magnetoconductivity, whereas no such effect is detected for the zero-field paraconductivity. The above anomalies are attributed to a nonuniform critical temperature distribution inside our samples and can be well explained assuming a Gaussian distribution of ${\mathit{T}}_{\mathit{c}}$'s with a standard deviation \ensuremath{\delta}${\mathit{T}}_{\mathit{c}}$=2.3 K. The excess Hall effect caused by superconducting fluctuations is negative in the entire accessible temperature range, which indicates, together with the paraconductivity and magnetoconductivity results that the indirect (Maki-Thompson) fluctuation process for (Bi,Pb${)}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$ is vanishingly small at temperatures from ${\mathit{T}}_{\mathit{c}}$ to 130 K.