Hall effect in the quasi two-dimensional organic superconductor κ-(BEDT-TTF)²Cu(NCS)₂

Hall effect measurements in the vortex state of the quasi two-dimensional organic superconductor κ-(BEDT-TTF)₂Cu(NCS)₂ are reported. A sign reversal phenomenon of the Hall resistivity is observed in the vortex state. The Hall conductivity changes monotonically with field and temperature in the vortex state, which is in contrast to the peak of the Hall resistivity observed there. The Hall conductivity is described as σ_xy = σ_xyⁿ + σ_xy^f, where σ_xyⁿ results from the quasiparticle and σ_xy^f the motion of the vortex. The expression has been theoretically proposed. In low fields, σ_xy^f is dominant in the Hall conductivity, which diverges to infinity as -1/(H - H*), where H* is a characteristic field in which the resistivity becomes zero.