c-axis magnetoconductivity of anisotropic superconducting single crystals: The density-of-states fluctuation scenario

The role of density of states fluctuations in the normal state properties of highTcsuperconductors

“…Very recently, similar measurements have been performed on single crystals of the very anisotropic Tl 2223 compound [185]. A strong negative magnetoresistance is observed a few degrees above Tc, initially increasing as temperature is decreased and then turning to positive as Tc is approached.…”

“…In contrast to the ab-plane magnetoresistance which is positive at all temperatures, along the c-axis the magnetoresistance has been found to have a negative sign not too close to Tc0 in many HTS compoundsÐ i.e. BSSCO [5,37,148,149], LSCO [150], YBCO [6] and TBCCO [185]Ð and turn to positive values at lower temperatures. We will show how these behaviours ® nd their explanation within thē uctuation theory in the magnetic-® eld induced suppression of the AL contribution along the c-axis.…”

“…Moreover, its competition with the positive Aslamazov± Larkin magnetoresitance gave good grounds for the prediction of a sign change in the magnetoresistance as temperature decreases towards Tc [39]. The latter e ect was very recently con® rmed experimentally on YBCO [6] and TBCCO [185] samples.…”

Possible dominance of the Maki–Thompson process in the fluctuation conductivity of Bi-2212 superconducting whiskers

“…About the MT terms, their contribution was reliably investigated only recently, after that the importance of the DOS term was completely understood. 8 These experiments, performed both in a magnetic field 9,10,11,12,13 and in zero field, 12,14 share the conclusion that the MT process is unimportant. The purpose of the present work is to show that an accurate analysis of the zero-field paraconductivity measured in ideal experimental conditions can lead to very different conclusions, setting the anomalous MT term as the most important throughout the whole temperature range of validity of the superconducting fluctuation model.…”

“…21 This implies a ratio T c /Θ D ≈ 0.3, which corresponds to a temperature range where no deviation from linearity is observed in the most common metals. The problems involved in this assumption have been often overcome by the measurement of the in-field paraconductivity ∆σ (B, T ) = 1/ρ a (B, T )−1/ρ a (0, T ), 8,9,10,11,12,13,22,23,24,25,26,27 but in principle a drawback in this approach is the possible presence of ordinary magnetoresistance effects, which add to superconducting fluctuations. 25 On the other hand, it has been recently reported 12 that the simple assumption of a linear T dependence leads to the same conclusions.…”