Correlation-Driven 3d Heavy Fermion Behavior in LiV₂O₄

Abstract LiV 2 O 4 is a spinel-structured compound that stands out as the first known 3d-electron system exhibiting typical heavy fermion behavior. A central question is how such strong mass renormalization emerges in the absence of f-electrons. In this work, we investigate the three-dimensional electronic structure of LiV 2 O 4 thin films using angle-resolved photoemission spectroscopy. We identify that an electron-like flat band is derived from a 1g orbitals, along with a highly dispersive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>e</mml:mi> <mml:mi mathvariant="normal">g</mml:mi> <mml:mo>′</mml:mo> </mml:msubsup> </mml:mrow> </mml:math> band strongly coupled with phonons. The overall agreement with dynamical mean-field theory calculations highlights the essential role of inter-orbital Hund’s coupling in reducing the a 1g bandwidth to 25 meV, approaching a Mott state. Notably, we find that heavy-fermion behavior arises from additional renormalization at the a 1g band near the Fermi level, likely driven by many-body interactions at energy scales down to a few meV and potentially linked to geometric frustration inherent to the spinel lattice. These results provide crucial insights into the origin of the heavy fermion behavior in 3d-electron systems.