Kateryna Foyevtsova (Notre Dame)
Date: Mon. April 20th, 2026, 12:45 pm-1:45 pmLocation: rockefeller 221 (Foldy Room) & Zoom
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Molecular physics without molecules in flat-band quantum materials
Kateryna Foyevtsova
Assistant Professor, University of Notre Dame
(Host: Walter Lambrecht)
Abstract: We all are familiar with molecular states in stable clusters of atoms called molecules (H2, H2O, C₈H₁₀N₄O₂, etc.) that form as quantum superpositions of the atoms’ individual wavefunctions. Their energies can be lower than those of the participating atomic states (commonly referred to as orbitals) which gives rise to chemical bonding, the cornerstone phenomenon in the chemical and biological sciences. Surprisingly, certain non-trivial quantum interference effects can lead to the formation of molecular orbital (MO) like states in inorganic crystalline solids without identifiable molecular clusters in their crystal structure. When involved in low-energy physics, MOs often give rise to intriguing physical effects such as flat bands in the electronic structure, expanding experimentally accessible regions of quantum phase diagrams and providing new ways to tune material properties. In this talk, I will present two examples of quantum MO systems: (1) Ti4MnBi2, a one dimensional metallic spin-½ system [1], and (2) La3Ni2O7, a member of the most recently discovered Ni-based family of high-temperature superconductors [2]. Using these examples, I will attempt to not only illustrate the rich physics of MOs in action but also highlight the challenges that such systems pose at various levels of condensed matter theory.
[1] X.Y. Li, A. Nocera, K. Foyevtsova, et al. Frustrated spin-1/2 chains in a correlated metal. Nat. Mater. 24, 716–721 (2025).
[2] K. Foyevtsova, I. Elfimov, and G. A. Sawatzky. Charge distribution and magnetism in bilayer La3Ni2O7: A hybrid functional study. Phys. Rev. B 112, 235163 (2025).