In-plane Hall-effect anisotropy in the organic superconductor κ-(BEDT-TTF)₂Cu[N(CN)₂]Br

Anisotropy of the Hall effect within the highly conducting plane has been measured in the organic superconductor κ-(BEDT-TTF)₂Cu[N(CN)₂]Br. Anisotropy and magnetic field dependence nonlinearity in the Hall resistivity are found above approximately 30 K. This behavior is shown to originate from an electron sheet of the Fermi surface. The temperature at which anisotropy and nonlinearity appear correlates with the temperature at which resistivity is at its maximum. The Hall effect behavior at temperatures below about 30 K corresponds to the predictions of the semiclassical weak-field model for a two-dimensional metal. A comparison of the Hall constant predicted by the calculated band structure within this model with the experimentally determined value revealed a large discrepancy. This is discussed within the framework of a reconstruction of the Fermi surface, as recently proposed by Weiss et al. on the basis of Shubnikov–de Haas effect studies under pressure.