Chemistry Weekly Seminar - Dr. Robert Green

Title:

Metal-insulator transitions and unconventional magnetic order in negative charge transfer oxides

Abstract:

In some correlated transition metal oxide compounds having high formal oxidation states, the observed cation orbital degrees of freedom are at odds with what is expected from the formal valence. As a consequence, holes are self-doped into ligand states and the materials are classified as negative charge transfer compounds, often having very different electronic structures and emergent properties than expected from the formal oxidation state picture. I will show that the trivalent perovskite nickel oxides are a clear example of such a material. Using a unique ligand field theory model in conjunction with synchrotron x-ray spectroscopy experiments, we have come to understand the origin of the novel electronic and magnetic phases of these nickelates [1,2], and have used this knowledge to tune new ground states useful for device applications [3,4].  Lastly, I will show that formally tetravalent iron oxides fall into this material class as well, and also exhibit very interesting electronic and magnetic phenomena [5].

References

1. Nat. Comm. 7, 13017 (2016)
2. Phys. Rev. B 94, 195127 (2016)
3. Nat. Phys. 14, 0197 (2018)
4. PNAS 115, 9515 (2018)
5. Phys. Rev. B(R) 98, 201115 (2018)