No abstract

Recently discovered superconductivity in hole-doped nickelate Nd 0.8 Sr 0.2 NiO 2 caught intensive attention in the field. An immediate question is how to improve its superconducting properties. Guided by the key characteristics of electronic structures of the cuprates and the nickelates, we propose that nickel chalcogenides with a similar lattice structure should be a promising family of materials. Using NdNiS 2 as an example, we find this particular crystal structure a stable one, through first-principle structural optimization and phonon calculation. We justify our proposal by comparing with CaCuO 2 and NdNiO 2 the strength of the charge-transfer characteristics and the trend in their low-energy many-body effective Hamiltonians of doped hole carriers. These analysis indicates that nickel chalcogenides host low-energy physics closer to that of the cuprates, with stronger magnetic interaction than the nickelates, and thus deserve further experimental exploration. Our proposal also opens up the possibility of a wide range of parameter tuning through ligand substitution among chalcogenides, to further improve superconducting properties.

Carrier density is one of the key controlling factors of material properties, particularly in controlling the essential correlations in strongly correlated materials. Typically, carrier density is externally tuned by doping or gating, and remains fixed below room temperature. Strangely, the carrier density in correlated semimetals is often found to vary sensitively to the external controls of small energy scale, such as temperature, magnetic field, and pressure. Here using the recently discovered nickelate superconductor as an example, we demonstrate a rather generic low-energy mechanism that short-range (non-collinear magnetic) correlation can reversely modulate the carrier density as well. Such a mutual influence between correlation and carrier density provides an extra ingredient for bifurcation of emergent phenomena. This special feature of correlated semimetals explains their versatile carrier density at low energy, and opens up new possibilities of functionalizing these materials.