Hund’s flat band in a frustrated spinel oxide

Electronic flat bands associated with quenched kinetic energy and heavy electron mass have attracted great interest for promoting strong electronic correlations and emergent phenomena such as high-temperature charge fractionalization and superconductivity. Intense experimental and theoretical research has been devoted to establishing the rich nontrivial metallic and heavy fermion phases intertwined with such localized electronic states. Here, we investigate the transition metal oxide spinel LiV<sub>2</sub>O<sub>4</sub>, an enigmatic heavy fermion compound lacking localized <i>f</i> orbital states. We use angle-resolved photoemission spectroscopy and dynamical mean-field theory to reveal a kind of correlation-induced flat band with suppressed interatomic electron hopping arising from intra-atomic Hund's coupling. The appearance of heavy quasiparticles is ascribed to a proximate orbital-selective Mott state characterized by fluctuating local moments as evidenced by complementary magnetotransport measurements. The spectroscopic fingerprints of long-lived quasiparticles and their disappearance with increasing temperature further support the emergence of a high-temperature "bad" metal state observed in transport data. This work resolves a long-standing puzzle on the origin of heavy fermion behavior and unconventional transport in LiV<sub>2</sub>O<sub>4</sub>. Simultaneously, it opens a path to achieving flat bands through electronic interactions in <i>d</i>-orbital systems with geometrical frustration, potentially enabling the realization of exotic phases of matter such as the fractionalized Fermi liquids.

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Publication Details

Journal
Proceedings of the National Academy of Sciences
Published
2025-11-06
DOI
https://doi.org/10.1073/pnas.2518213122
Primary Topic
Physics of Superconductivity and Magnetism
Type
article
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article

Hund’s flat band in a frustrated spinel oxide

Alexander Hampel, Joshua P. Wakefield, Giorgio Sangiovanni, Eli Rotenberg et al.
Proceedings of the National Academy of Sciences
Physics of Superconductivity and Magnetism
article

Hund’s flat band in a frustrated spinel oxide

Alexander Hampel, Joshua P. Wakefield, Giorgio Sangiovanni, Eli Rotenberg, Olivier Parcollet, Marta Zonno, Craig Polley, Steef Smit, Mats Leandersson, M. Grundner, Asish K. Kundu, Chris M. Jozwiak, Matteo Crispino, Joseph George Checkelsky, E. Vescovo, Aaron Bostwick, Masahiko Isobe, Riccardo Comin, Dongjin Oh, Manish Verma, Fabian B. Kugler, A. Damascelli, H. Takagi, Sergey Gorovikov, Antoine Georges, Peter Moen, Xiangyu Luo, Ulrich Schollwöck, Anil Rajapitamahuni
article en

Abstract

Electronic flat bands associated with quenched kinetic energy and heavy electron mass have attracted great interest for promoting strong electronic correlations and emergent phenomena such as high-temperature charge fractionalization and superconductivity. Intense experimental and theoretical research has been devoted to establishing the rich nontrivial metallic and heavy fermion phases intertwined with such localized electronic states. Here, we investigate the transition metal oxide spinel LiV<sub>2</sub>O<sub>4</sub>, an enigmatic heavy fermion compound lacking localized <i>f</i> orbital states. We use angle-resolved photoemission spectroscopy and dynamical mean-field theory to reveal a kind of correlation-induced flat band with suppressed interatomic electron hopping arising from intra-atomic Hund's coupling. The appearance of heavy quasiparticles is ascribed to a proximate orbital-selective Mott state characterized by fluctuating local moments as evidenced by complementary magnetotransport measurements. The spectroscopic fingerprints of long-lived quasiparticles and their disappearance with increasing temperature further support the emergence of a high-temperature "bad" metal state observed in transport data. This work resolves a long-standing puzzle on the origin of heavy fermion behavior and unconventional transport in LiV<sub>2</sub>O<sub>4</sub>. Simultaneously, it opens a path to achieving flat bands through electronic interactions in <i>d</i>-orbital systems with geometrical frustration, potentially enabling the realization of exotic phases of matter such as the fractionalized Fermi liquids.

Proceedings of the National Academy of SciencesVol. 122(45)
University of Stuttgart (DE), University of Geneva (CH), Centre National de la Recherche Scientifique (FR), University of British Columbia (CA), École Polytechnique (FR), Lawrence Berkeley National Laboratory (US), University of Cologne (DE), Collège de France (FR), Brookhaven National Laboratory (US), University of Würzburg (DE), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris-Saclay (FR), Center for Theoretical Physics (PL), Max Planck Institute for Solid State Research (DE), Complexity, Topology and Dynamics in Quantum Matter (DE), Centre de Physique Théorique (FR), Instituto de Física Teórica (ES), Center for Integrated Quantum Science and Technology (DE), MAX IV Laboratory (SE), Munich Center for Quantum Science and Technology (DE), Flatiron Health (United States) (US), Centre de Physique Théorique (FR), Flatiron Institute (US), Massachusetts Institute of Technology (US), The University of Tokyo (JP), Ludwig-Maximilians-Universität München (DE), Canadian Light Source (Canada) (CA)
Openalex Percentile: Top 79%
Physics of Superconductivity and Magnetism
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