Dualism of the 4f electrons and its relation to high-temperature antiferromagnetism in the heavy-fermion compound YbCoC2

We report on the study of the noncentrosymmetric ternary carbide ${\mathrm{YbCoC}}_{2}$. Our magnetization, specific heat, resistivity, and neutron diffraction measurements consistently show that the system behaves as a heavy-fermion compound, displaying an amplitude-modulated magnetic structure below the N\'eel temperature reaching ${T}_{\mathrm{N}}=33$ K under pressure. Such a large value, being the highest among the Yb-based systems, is explained in the light of our ab initio calculations, which show that the $4f$ electronic states of Yb have a dual nature, i.e., due to their strong hybridization with the $3d$ states of Co, $4f$ states expose both localized and itinerant properties.