Unconventional Anomalous Hall Effect in the Metallic Triangular-Lattice Magnet<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>PdCrO</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>

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.