Emergent electronic phases in Ruddlesden-Popper chromium oxide perovskites

Chromium-based compounds realize a multitude of electronic and magnetic phases: half-metals (CrO₂), ferromagnetic insulators (CrI₃, YCrO₃), antiferromagnetic insulators (Cr₂Se₃, CrSe₂, Cr₂O₃ and LaCrO₃), or antiferromagnetic metals (Cr and SrCrO₃). These compounds, whose magnetic transitions are often near room temperature, represent a far less charted platform for emergent quantum matter compared to their other 3d transition metal siblings.
Low-dimensional perovskites of tetravalent chromium deserve particular attention as they uniquely realize a strongly-correlated electron system with d² electronic configuration and active spin and orbital degrees of freedom. Antiferromagnetism is ubiquitous in these systems, but recent theoretical studies indicate the presence of proximate electronic phases, including orbital order and superconductivity. These materials cannot be easily stabilized in bulk form and in the Cr⁴⁺ oxidation state (with spin S=1) but could host interesting new phenomena enabled by the strong interplay of spin, charge, and orbital degrees of freedom.
To explore these scientific opportunities, we have grown thin films of various members of the Ruddlesden-Popper series of chromium oxide perovskites: SrCrO₃, Sr₂CrO₄, and Sr4Cr₃O₁₀. In this talk, I will report on the synthesis and characterization of their transport and magnetic properties, including recent investigations of spin and orbital ordering in the ground state of these materials.