Superconductivity of Jahn–Teller Magnets

The search for new oxide superconductors that has been undertaken by Bednorz and Müller and culminated in the discovery of high-temperature superconductivity (HTSC) in cuprates, has been based on the idea of creating conducting oxides containing Jahn–Teller (JT) ions, which are characterized by strong electron–lattice coupling with the formation of polarons and bipolarons. This idea is not currently considered among the leading mechanisms of HTSC. However, almost all HTSC or similar exotic superconducting materials based on 3d or 4d ions known today are JT magnets (cuprates La2CuO4, nickelates such as RNiO2 and La3Ni2O7, ferropnictides/chalcogenides, Sr2RuO4, and RuO2). Unlike the idea of Bednorz and Müller, we believe that the superconductivity of Jahn–Teller magnets is not related to the Jahn–Teller effect, but it is due to their intrinsic charge instability with respect to so-called anti-JT disproportionation. In this review, an original method of charged triplets for describing the electronic and magnetic structure of JT magnets beyond the Hubbard model and density functional theory with examples of phase diagram modeling has been discussed.