HALL-EFFECT IN THE MIXED-STATE OF SUPERCONDUCTING L(1.85)CE(0.15)CUO(4) (L=ND,SM) SINGLE-CRYSTALS

The temperature and field dependencies of the Hall voltage in the mixed and in the normal state of supeconducting L1.85Ce0.15CuO4 (L=Nd and Sm) single crystals have been measured. Crystals having different critical temperatures (15<Tc<20 K) and transition widths (0.5<Tc<3 K) have been used in order to explore the effects of crystal quality on the controversial mixed-state Hall effect. In spite of the cerium doping, the normal-state Hall coefficient is found to be positive at low temperatures (TTc) for all measured crystals. At higher temperatures (TTc), the Hall coefficient becomes negative. In the mixed state, the Hall resistivity displays an anomalous xy(H) peak. However, in contrast to what has been found in other high-Tc superconductors, the polarity of the anomaly can have, depending on temperature, either the same sign or opposite to the Hall effect in the normal state, just above Tc. The appearance of the xy(H) anomaly is not ubiquitous but is only observed in crystals of narrow transition widths. To account for these results we explore several of the possible explanations that have been already proposed. © 1994 The American Physical Society.