Walter Lambrecht (CWRU)

Date: Mon. September 29th, 2025, 12:45 pm-1:45 pm
Location: Zoom & Rockefeller 221 (Foldy room)

Correlated electronic structure and magnetism in complex oxides: alkalicobaltates and vanadates

Walter Lambrecht

Department of Physics, Case Western Reserve University

Abstract: LiCoO₂ is a well known cathode in Li batteries and it  is a simple band insulator due to its octahedral coordination of Co, but nonetheless has some interesting surface and optical properties. NaCoO₂ becomes a superconductor if we expand the distance between the layers. Is this related to the surface properties? What about even larger alkali ions  like K (potassium)? KCoO₂ has different crystal structures with square pyramidal or tetrahedral coordination. We studied how Co³⁺ with d⁶ in these unusual coordinations leads to interesting magnetic properties. Its P4/nmm structure is found to be an antiferromagnet with large magnetic moments, large excitonic effects  and a structure closely related to that of the high Tc cuprates with square Co-O motives. In another structure, the 2d structure, KCoO₂ may be an altermagnet. It shares this structure with chalcopyrite MnGeP₂, which we recently studied and found to be also an altermagnet but with much large magnetic moment. In the last part of the talk, I will discuss bronzes of V₂O₅ like LiV₂O₅ and NaV₂O₅. The half filling of the d_xy like lowest conduction band here leads to charge disproportionation as well as magnetic moments. We study the magnetic properties and spin waves of two structures, one with a symmetry breaking charge disproportionation into V⁴⁺ and V⁵⁺ (P2₁mn) and the other (Pmmn) with all equal V carrying half a Bohr magneton per V.  Along the way, I will explain how we calculated magnetic exchange interactions from the transverse spin susceptibility based on quasiparticle self-consistent GW band structures.

 

Host: Shulei Zhang