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At temperaturesTmuch lower than its superconducting critical temperatureTc= 2.1 K, the heavy fermion superconductor UTe2has a unique phase diagram of magnetic fieldHvs. φ and θ, anglesHis tilted from theb-axis toward thea- andc-axes, respectively, of its orthorhombic unit cell. The phase diagram contains three distinct superconducting phases: SC1in which φ and θ extend from 0 to 90° andH≤ ~15 T; SC2for φ ≤ ~7°, θ ≤ ~4° and ~15 T ≤H≤Hm= ~35 T, the onset of the magnetic field polarized (FP) phase, and SCFPwhich resides entirely within the FP phase in a pocket of superconductivity extending from θ ≈ 20° to 40° and from ~40 T to above 60 T. We studied the evolution of theHvs. θ phase diagram for Th concentrations 0.005 ≤x≤ 0.047 in the U1-xThxTe2system at ~0.6 K. Within this range ofxvalues, SC1extends over 0 ≤ θ ≤ 90° andH≤ ~10 T forx= 0.047, while SC2is suppressed. The SCFPand FP phases are unaffected tox= 0.02 but are completely suppressed in the regionx= 0.025 to 0.047 where the residual resistance ratioRRR~3 indicates a significant amount of disorder. These results complement recent studies of nonsuperconducting disordered UTe2single crystals in which the SC1and SC2phases are absent, but the FP and so-called “orphan” SCFPphases are retained.
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This content will become publicly available on November 11, 2026
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 LiV2O4, an enigmatic heavy fermion compound lacking localizedforbital 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 LiV2O4. Simultaneously, it opens a path to achieving flat bands through electronic interactions ind-orbital systems with geometrical frustration, potentially enabling the realization of exotic phases of matter such as the fractionalized Fermi liquids.
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- Award ID(s):
- 2104964
- PAR ID:
- 10650538
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- PNAS
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 122
- Issue:
- 45
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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