Hall-effect measurements below 20 K and up to 23 T on single crystals of the organic conductor α-(BEDT-TTF${)}_2$KHg(SCN${)}_4$ are reported. The sign of the Hall coefficient ${\mathit{R}}_{\mathit{H}}$ is positive in the whole temperature range, indicating a hole carrier. ${\mathit{R}}_{\mathit{H}}$ obtained from the H-linear dependence of the Hall resistance ${\mathit{R}}_{\mathit{x}\mathit{y}}$ steeply increases below 10 K and saturates around 4 K. This increase in ${\mathit{R}}_{\mathit{H}}$ coincides with anomalies observed in the static magnetic susceptibility and the electrical resistance at about 10 K. This finding suggests a reconstruction of the Fermi surface associated with the spin-density-wave (SDW) gap formation in this magnetic-phase transition. The high-field ${\mathit{R}}_{\mathit{x}\mathit{y}}$ above about 10 T at 4.2 K deviates from the H-linear dependence, suggesting that the SDW formation might change with fields.

• Received 31 March 1993

DOI:https://doi.org/10.1103/PhysRevB.48.1928