Unconventional anomalous hall effect in the metallic triangular-lattice magnet PdCrO₂.

We experimentally reveal an unconventional anomalous Hall effect (UAHE) in a quasi-two-dimensional triangular-lattice antiferromagnet PdCrO₂. Using high quality single crystals of PdCrO₂, we found that the Hall resistivity ρ(xy) deviates from the conventional behavior below T*≃20 K, noticeably lower than T(N)=37.5 K, at which Cr³+ (S=3/2) spins order in a 120° structure. In view of the theoretical expectation that the spin chirality cancels out in the simplest 120° spin structure, we discuss required conditions for the emergence of UAHE within Berry-phase mechanisms.