Anomalous Magnetotransport Induced by Spin Fluctuations in the Metallic Delafossite Triangular-Lattice Antiferromagnet PdCrO₂

ABO₂ delafossite materials are of high interest due to their fascinating physical properties, such as record-breaking oxide electrical conductivity, and emergent magnetic states related to geometrical frustration. Recent studies on PdCrO₂, a metallic delafossite triangular-lattice antiferromagnet (T_N ≈ 38 K), have uncovered an unconventional anomalous Hall effect, with origins that remain poorly understood. Here, we utilize wide-temperature-range X-ray diffraction, inelastic neutron scattering, magnetic pair distribution function analysis, muon spin relaxation, magnetometry, and magnetotransport measurements on high-quality chemical vapor transport (CVT)-grown PdCrO₂ single crystals to elucidate the role of frustrated spin fluctuations above T_N in anomalous structural and magnetotransport behavior. PdCrO₂ is the first metallic delafossite to exhibit a large and unusual c-axis negative thermal expansion (-5 ppm/K) up to 300 K, likely related to short-range magnetic fluctuations. Most surprisingly, both the anomalous Hall effect and magnetoresistance in PdCrO₂ persist far above T_N, connecting to the negative thermal expansion and suggesting a possible role for chiral spin-clusters.