The normal state Hall effect in Nd1−2xCaxMxBa2Cu3O7−δ (M = Pr, Th): Evidence for hole localization by disorder

The transport properties of sintered samples of Nd1−2xCaxMxBa2Cu3O7−δ (M = Pr, Th) with 0 ⩽ x ⩽ 0.10 have been studied in the normal state by Hall effect measurements. The Hall coefficient at high temperature was almost constant for Ca-Pr while it increased with increasing Ca-Th doping concentration. The results for the Hall coefficient as a function of temperature and doping concentration were analyzed within two different models. A good agreement between models and data was obtained. On the basis of these models, it was inferred that Ca-Pr and Ca-Th doping introduce electronic disorder in the CuO2 planes. The localization tendency is driven by electronic disorder. This is the main reason for strong depression of the superconducting critical temperature in both alloys. It was found that the Hall angle is proportional to T2 in the whole measured temperature range in Ca-Pr doped samples while there are deviations at high temperature in the Ca-Th doped series. In a phenomenological narrow band model, the conduction band was asymmetric for the pure sample and this asymmetry decreased with increasing Ca-Th doping while it was almost constant for Ca-Pr doped samples.