Anomalous metallic state in quasi-two-dimensional BaNiS2

We report on a systematic study of the thermodynamic, electronic, and charge transport properties of high-quality single crystals of BaNiS2, the metallic end member of the quasi-two-dimensional BaCo1−xNixS2 system characterized by a metal-insulator transition at xcr=0.22. Our analysis of magnetoresistivity and specific heat data consistently suggests a picture of compensated semimetal with two hole bands and one electron band, where electron-phonon scattering dominates charge transport and the minority holes exhibit, below ∼100 K, a very large mobility, μh∼15000cm2V−1s−1, which is explained by a Dirac-like band. Evidence of unconventional metallic properties is given by an intriguing crossover of the resistivity from a Bloch-Gruneisen regime to a linear-T regime occurring at 2 K and by a strong linear term in the paramagnetic susceptibility above 100 K. We discuss the possibility that these anomalies reflect a departure from conventional Fermi-liquid properties in presence of short-range AF fluctuations and of a large Hund coupling.