T.R. Chien

Anomalous magnetoresistance and Hall current in the normal state of the cuprate superconductors

Abstract Experiments on the normal-state Hall effect in YBa2Cu3O7 and the normal-state magnetoresistance in Bi2Sr2CuO6(Bi 2201) are described. The strong temperature dependence of the Hall resistivity is shown to derive from a ‘Hall scattering rate’ 1/τH that varies as the square of temperature, in contrast to the transport scattering rate 1/τtr. Scattering from zinc impurities increases both rates. We compare our results with a recent theory of Anderson. Low-temperature magnetoresistance (MR) has been used to extract the dephasing rate 1/τφ in single-crystal Bi 2001. Between 0.4 and 20 K, 1/τφ varies as T 1 3 . We discuss the anomalous enhancement of the dephasing rate and implications for the usual quasi-particle picture. The MR in a longitudinal field shows novel features that do not fi t conventional interaction theory.

Discontinuous jump in transverse magnetization of the flux lattice in YBa2Cu3O7 crystals observed by torque magnetometry

Abstract We have measured the torque in YBa2Cu3O7 crystals when the applied field is rotated at angle to the c-axis in the superconducting state. Below a characteristic field Hm we observe a novel discontinuity in the transverse magnetization when exceeds 90°. We interpret this jump as a giant reconfiguration of the flux lattice in response to the field rotation.

Temperature dependent Hall effect in Nd2−xCexCuO4 and “60 K” YBa2Cu3Oy single crystals

Abstract The Hall coefficient is studied in single crystals of the two superconductors Nd2−xCexCuO4 and “60 K” YBa2Cu3Oy. The strong temperature dependence is discussed. We also report the temperature dependence of the out-of-plane resistivity in the latter.

The Hall Effect and Magnetoresistance of the High-Temperature Cuprate Superconductors

We show that underlying the unusual temperature dependence of R H is a Hall angle damping rate which varies as T 2, in contrast with the linear-T dependence in the transport scattering rate. The effect of impurities on this rate is discussed. The dephasing rate for carriers in Bi 2201 is measured by low temperature magnetoresistance, and found to vary as the cube root of T from 0.4 to 20 K. Spin dependent effects in the magnetoresistance are discussed.

Transition from activated to diffusive behavior in the vortex-liquid state in YBa2Cu3O7

Abstract In the vortex-liquid state in YBa 2 Cu 3 O 7 , there exist two distinct dissipative states separated by a field H > k . Below H k , the resistivity is strongly field-activated, with a prefactor that is anomalously enhanced over the normal-state resistivity ϱ N by ≈12 orders of magnitude. At H k , the prefactor collapses to a temperature-independent value equal to ϱ N , and the vortex motion becomes diffusive. The existence of the H k boundary is also reflected in the anomalous behavior of the Hall resistivity.

Carrier Scattering Rates Measured by Hall Effect and Magnetoresistance in the High-Tc Oxides

Transport measurements are a useful way to probe the electronic properties of the oxide superconductors because they couple directly to the relevant charge excitations. The unusual linear-temperature variation of the resistivity has received much attention. However, other transport properties are also anomalous when compared with conventional metal behavior. In this report, we survey some recent Hall effect and magnetoresistance measurements on single crystals of YBa2Cu3O7 (YBCO) and Bi2Sr2CuO6 (Bi 2201).

Tunneling and Transort Experiments on Single-Crystal Nd2-xCexCuO4-y and YBa2Cu3O7

Several anomalous features are observed in tunneling spectra obtained on cleaved crystals of Nd2-xCexCuO4-y. The conductance curve is strongly asymmetric in the bias, and the gap parameter △ increases as the temperature is wanned towards T c . In one sample a weak magnetic field completely suppress distinctive structures which appear at energies above the gap. Hall measurements in Nd2-xCexCuO4-y crystals at low temperatures provide strong evidence for an anomalous contribution to the Hall scattering in the normal state. The Andreev reflection spectrum in YBa2Cu3O7 crystals is also reported.

Andreev Reflection, Thermal Conductivity, Torque Magnetometry, and Hall Effect Studies on High-Tc Systems

We survey recent experiments which probe the interface between the high-T c oxides and Au (Andreev reflection, and proximity induced superconductivity). We also discuss experiments which measure the anisotropy of 123 (thermal conductivity, torque magnetometry) and the Hall effect in the Bi- and Tl-based superconductors.