Heavy fermions are typically associated with f-electron Kondo systems but have been proposed to play a role also in d-electron systems, despite the observation of a flat d-orbital band near the Fermi level is elusive. Here, the authors use angle-resolved photoemission spectroscopy to reveal flat bands near the Fermi level in Fe5−xGeTe2, demonstrating Kondo physics behavior and a transition from non-Fermi-liquid to a heavy mass Fermi-liquid state.
- Soonsang Huh
- Kaishu Kawaguchi
- Takeshi Kondo
