Observation of Flat Bands and Dirac Cones in a Pyrochlore Lattice Superconductor

Abstract

Emergent phases often appear when the electronic kinetic energy is comparable to the Coulomb interactions. One approach to seek material systems as hosts of such emergent phases is to realize localization of electronic wavefunctions due to the geometric frustration inherent in the crystal structure, resulting in flat electronic bands. Recently, such efforts have found a wide range of exotic phases in the two-dimensional kagome lattice, including magnetic order, time-reversal symmetry breaking charge order, nematicity, and superconductivity. However, the interlayer coupling of the kagome layers disrupts the destructive interference needed to completely quench the kinetic energy. Here we demonstrate that an interwoven kagome network-a pyrochlore lattice-can host a three dimensional (3D) localization of electron wavefunctions. Meanwhile, the nonsymmorphic symmetry of the pyrochlore lattice guarantees all band crossings at the Brillouin zone X point to be 3D gapless Dirac points, which was predicted theoretically but never yet observed experimentally. Through a combination of angle-resolved photoemission spectroscopy, fundamental lattice model and density functional theory calculations, we investigate the novel electronic structure of a Laves phase superconductor with a pyrochlore sublattice, CeRu${}_2$. We observe flat bands originating from both the Ce 4$f$ orbitals as well as from the 3D destructive interference of the Ru 4$d$ orbitals. We further observe the nonsymmorphic symmetry-protected 3D gapless Dirac cones at the X point. Our work establishes the pyrochlore structure as a promising lattice platform to realize and tune novel emergent phases intertwining topology and many-body interactions.

27 pages, 4 figures

References in corpus (15)

• The electronic properties of graphene
• High temperature fractional quantum Hall states
• Fractional quantum Hall states at zero magnetic field
• Nearly-flat bands with nontrivial topology
• Classification of stable three-dimensional Dirac semimetals with nontrivial topology
• Pyrochlore Photons: The U(1) Spin Liquid in a S=1/2 Three-Dimensional Frustrated Magnet
• Superconductivity in the ${\mathbb{Z}}_2$ kagome metal KV${}_3$Sb${}_5$
• Discovery of charge density wave in a correlated kagome lattice antiferromagnet
• Rotation symmetry breaking in the normal state of a kagome superconductor KV3Sb5
• Strongly correlated flat-band systems: The route from Heisenberg spins to Hubbard electrons
• Exotic electronic states in the world of flat bands: from theory to material
• Quantum Spin Ice Dynamics in the Dipole-Octupole Pyrochlore Magnet Ce${}_2$Zr${}_2$O${}_7$
• Discovery of charge order and corresponding edge state in kagome magnet FeGe
• Weyl semimetal from spontaneous inversion symmetry breaking in pyrochlore oxides
• Nonsymmorphic Symmetry-Protected Band Crossings in a Square-Net Metal PtPb${}_4$

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• Finite temperatures and flat bands: the Hubbard model on three-dimensional Lieb lattices
• Many-body electronic structure in pyrochlore superconductor CsBi2 and spin liquid Pr2Ir2O7
• Dichotomy of flat bands in the van der Waals ferromagnet Fe${}_5$GeTe${}_2$
• Frustration-free free fermions