Hall Effect in the Superconducting State of Superclean Superconductors

在超净超导体中，准粒子能级的宽度比超导带隙窄，涡旋动力学被认为与传统超导体有很大的不同。高温超导体是这类超导体的最佳候选者之一。霍尔效应中众所周知的反常现象，包括混合态霍尔系数的符号变化，可以归因于这类超导体的这一特殊特性。考虑到这一点，我们开展了以下三个与高温超导体霍尔效应有关的实验：(1)载流子掺杂对霍尔效应符号变化的依赖；(2)低温临界场分布的场依赖；(3)涡旋运动粘性的测量。(1)通过连续改变载流子掺杂水平，系统地测量了给定样品的霍尔系数的符号变化，发现即使在轻微过度掺杂的区域，霍尔系数的符号变化也是持续的。为了更好地定量分析霍尔效应，我们分析了霍尔电导率sigma&lt；xy‘&gt；并阐明了磁芯中涡旋运动和准粒子的贡献与温度的关系。(2)尽管YBa2Cu3O；7-y&gt；7-y&gt；8+y*S&gt；8+y*YBa2Cu3O7-y&gt；7-y&gt；(3)为了定量估计涡旋运动的粘度，我们测量了Bi2Sr2CaCu2O&lt；8+y*&gt；的表面电阻(R_S)与场的关系。我们在YB_2Cu3O_7-y&gt；中观察到了R_S**H的特征场依赖关系。

In superclean superconductors, where the width of quasi-particle level is narrower than the superconducting gap, vortex dynamics is believed to be quite different compared with conventional superconductors. High temperature superconductors are one of the best candidates of this class of superconductors. The well known anomaly in the Hall effect including sign change of Hall coefficient in the mixed state can be attributed to this special feature of this class of superconductors.With this in mind, we carried out the following three experiments related to Hall effects in high temperature superconductors ; (1)Carrier-doping dependence of the sign change of the Hall effect (2)Field dependence of low temperature critical field profile and (3)Measurement of viscosity of vortex motion.(1)With a systematic measurements of Hall effect in a given sample by changing the carrier doping level successively, we find out that the sign change in the Hall coefficient is sustained even in the slightly overdoped region. In order to make more quantitative analysis of Hall effect, we analyzed Hall conductivity sigma_<xy'> and clarified the temperature dependence of the contributions from vortex motion and quasi-particles in the core. (2)Despite the reported huge rotation of the critical state field profile in YBa_2Cu_3O_<7-y> at low temperature, possibly due to extremely large Hall angle, we have not observed any sign of the rotation of the profile neither in YBa_2Cu_3O_<7-y> nor Bi_2Sr_2CaCu_2O_<8+y*s>. (3)For the quantitative estimation of viscosity for vortex motion, we measured field dependence of surface resistance (R_S) in Bi_2Sr_2CaCu_2O_<8+y*>. We find a characteristic field dependence of R_S**H as observed in YB_2Cu_3O_<7-y>.