Superconducting fluctuations inBi2Sr2

W. Lang

¹

,

G. Heine

²

,

Witold Kula

³

et al.

Abstract

A detailed study of normal-state magnetotransport properties in (Bi,Pb)~Sr2Ca2Cu30 thin films with a zero-resistance critical temperature T,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 Auctuations, using theories for two-dimensional, layered superconductors.We have obtained a consistent set of parameters, i.e. , the in-plane coherence length g,b(0) =1.6 nm, the out-of-plane coherence length g, (0) =0.14 nm, and the electron-hole asymmetry parameter P= -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 T, s with a standard deviation 6T, =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) Auctuation process for (Bi,Pb)2Sr2Ca2Cu30" is vanishingly small at temperatures from T, to 130 K.(2D) to three-dimensional (3D) behavior in the vicinity of T, can be estimated. There has been a considerable discussion whether the results in YBa2Cu307 indicate a 2D behavior, ' with a possible crossover to 3D, or isotropic superconductivity. This question is of substantial interest with regard to the role of coupling along the c axis in the superconducting state.

Hall effect in superconducting films

“…17 and 16). This change in sign of the corrections cannot explain the change in sign of the Hall coefficient observed in various superconductors in the mixed state [29][30][31][32][33] as the analysis in terms of gaussian fluctuations is not applicable in this regime.…”

Superconductivity in a system with preformed pairs

“…The extensive study [16] of the fluctuation regime in [33]. These data indicate that hydrodynamic approach is likely to be valid but do not allow to make a definite conclusion.…”

“…This sign change is preempted by the negative fluctuational contribution to the positive Hall effect in the normal state [16,17]; qualitatively both the sign change in the superconducting phase and the fluctuational Hall effect can be explained if Cooper pairs which are responsible for superconductivity are in fact negatively charged. In this case these pairs give a large negative contribution to the Hall conductivity in the vortex state below T c which is proportional to 1/B; and produce negative fluctuational Hall conductivity observed in [16]. Both Hall conductivity in the vortex state near T c and the fluctuational conductivity above it can be described in the framework of the time dependent Ginzburg Landau (TDGL) equation; for this equation the negative sign of the Cooper pair implies that the imaginary part of the relaxation rate Im γ < 0,…”

Fermi-level electronic structure of a topological-insulator/cuprate-superconductor based heterostructure in the superconducting proximity effect regime

“…Finally, BSCCO and other cuprate superconductors are known to have a short superconducting coherence length, especially along the out-of-plane direction (only less than 1 nm). 37 Thus even if the above conditions (lattice symmetries, k F , superconducting order parameters and pairing symmetries) between these two systems could be perfectly matched, the proximity induced superconductivity is not expected to propagate over a distance (film thickness larger than 1 or 2 QL) along the c-axis of BSCCO. In addition to these factors, the d-wave superconductivity in BSCCO can further destabilize the Majorana fermions at the interface, since Majorana modes can leak to the BSCCO substrate through the nodes (gapless) of the superconducting gap, causing dephasing or decoherence of the zero-bias modes.…”