Use of out-of-plane resistivity for determination of the 2D or 3D character of superconductive fluctuations for Bi-2212 crystals in the mixed state and origin of anomalous high out-of-plane resistivity for weakly oxidized crystals

The single crystal superconducting Bi-2212 whiskers fabrication and their thermal transport properties

“…6b with black solid line. Fitting parameters 0 and E were found to be 1.04 ± 0.002 and 12.7 ± 0.03 meV which are good agreement with previous studies in the literature [57].…”

Hole-Filling above Tc, at the Origin of the In-Plane Resistivity Anomaly in Bi-2212 Crystals

“…According to the first one, by [13,14], the phenomenon should be related to the superconducting transition itself: we would be dealing with an increase of the resistivity near T c due to the diffusion of free electrons by Cooper pairs. The second proposition, which we have made in [9,15], contests Balestrino's explanation and suggests another origin, not related to the superconducting transition but involving an increase of the Fermi level (hole-filling) with decreasing temperature. In this latter explanation the increase of resistivity corresponds to the first steps of a metal±insulator transition, and the law r c r 0 exp E=kT À T i (where T i is the temperature when the compounds turns to an insulator state) gives a perfect fit to the experimental results.…”

“…In this latter explanation the increase of resistivity corresponds to the first steps of a metal±insulator transition, and the law r c r 0 exp E=kT À T i (where T i is the temperature when the compounds turns to an insulator state) gives a perfect fit to the experimental results. We have shown [9,15] that the critical temperature T i depends on the oxidation degree of the crystals and that E ranges between 5 and 10 meV.…”

“…Recently, we investigated the strong increase of resistivity along the c-axis with decreasing temperature, just above T c , for underdoped Bi-2212 crystals, and we suggested that the phenomenon was a consequence of a slight shift of the Fermi level in the normal state [9,15]. If the Fermi level reaches the top of the valence band (hole-filling), it may produce a sudden and strong increase of r ab and r c .…”

Superconducting interaction charge in thallium-based high-TC cuprates: Roles of cation oxidation state and electronegativity

“…Since inner-layer cation vacancies, as in the case of Tl 1-x LaSrCuO 5 , tend to trap charge, they too contribute to the net transfer of carriers to the interacting outer layers, and thus would also introduce a γ-factor of 1/4 (weighted by their stoichiometric component). The ultimate physical effect of combining the increased valence and high Pauling electronegativities of Bi (2.02) and Pb (2.33) when compared to that of Cu (1.90) essentially suppresses participation of any inner-layer charges in the superconductivity, and is properly reflected by the insulating or semiconducting double BiO inner layers [29,30], large effective mass anisotropy ratios (m* c /m* ab ) of 1300 to 3000 [31,32], micaceous crystal morphology with prominent cleavage between BiO layers, and accommodation of intercalation molecules [26]. For the Tl-based cuprates, however, the comparatively low electronegativity of Tl (1.62) is too weak to adversely affect charge transfer along the hard-axis, resulting in a comparatively small mass anisotropy (e.g., 205 Tl NMR measurements reported in Ref.…”