Non-Fermi liquid behavior in a correlated flatband pyrochlore lattice

Abstract

Electronic correlation effects are manifested in quantum materials when either the onsite Coulomb repulsion is large or the electron kinetic energy is small. The former is the dominant effect in the cuprate superconductors or heavy fermion systems while the latter in twisted bilayer graphene or geometrically frustrated metals. However, the simultaneous cooperation of both effects in the same quantum material--the design principle to produce a correlated topological flat bands pinned at the Fermi level--remains rare. Here, using angle-resolved photoemission spectroscopy, we report the observation of a flat band at the Fermi level in a 3$d$ pyrochlore metal CuV${}_2$S${}_4$. From a combination of first-principles calculations and slave-spin calculations, we understand the origin of this band to be a destructive quantum-interference effect associated with the V pyrochlore sublattice and further renormalization to the Fermi level by electron interactions in the partially filled V $t_{2g}$ orbitals. As a result, we find transport behavior that indicates a deviation from Fermi-liquid behavior as well as a large Sommerfeld coefficient. Our work demonstrates the pathway into correlated topology by constructing and pinning correlated flat bands near the Fermi level out of a pure $d$-electron system by the combined cooperation of local Coulomb interactions and geometric frustration in a pyrochlore lattice system.

23 pages, 4 figures, to appear in Nature Physics

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• Quantum critical metals and loss of quasiparticles
• Electron correlations in the kagome flat band metal $\mathrm{CsC}{\mathrm{r}}_3\mathrm{S}{\mathrm{b}}_5$
• Exotic charge density waves and superconductivity on the Kagome Lattice
• A Recipe for Flat Bands in Pyrochlore Materials: A Chemist's Perspective
• Chemical enhancement of superconductivity in LaRu3Si2 with mode-selective coupling between kagome phonons and flat bands
• Hund flat band in a frustrated spinel oxide
• Observation of Resonance of Kagome Flat Band Doublet
• Ferromagnetism vs. Antiferromagnetism in Narrow-Band Systems: Competition Between Quantum Geometry and Band Dispersion
• Cubic Dirac Semimetals: General Theory and Application to Rare-Earth Magnets
• Many-body electronic structure in pyrochlore superconductor CsBi2 and spin liquid Pr2Ir2O7
• Electronic structures and magnetism in van der Waals flat-band material Ni${}_3$GeTe${}_2$
• Interorbital Antisymmetric Hopping Generated Flat Bands on Kagome and Pyrochlore Lattices
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• Experimental electronic phase diagram in a diamond-lattice antiferromagnetic system
• Quantum critical point followed by Kondo-like behavior due to Cu substitution in itinerant, antiferromagnet ${\text{La}}_2{\text{(Cu}}_x{\text{Ni}}_{1-x}{)}_7$
• Dichotomy of flat bands in the van der Waals ferromagnet Fe${}_5$GeTe${}_2$
• Site-selective correlations in interacting "flat-band" quasicrystals