Metallic quantum criticality enabled by compact molecular orbitals in frustrated-lattice systems

Flat or weakly dispersive bands emerge in a diverse array of materials, spanning twisted heterostructures and compounds with geometrically-frustrated lattices. Their small bandwidth amplifies the effect of electronic correlations. Moreover, these flat bands frequently reside within a topologically non-trivial active-band subspace. Recent experiments on kagome and pyrochlore metals have uncovered a rich variety of strong-correlation phenomena, including interaction-driven pinning of flat bands to the vicinity of the Fermi level, strange-metallic transport, and superconductivity emerging in the vicinity of a density-wave transition [1]. Here, we theoretically investigate the correlation phenomena in metals on lattices that realize destructive kinematic interference [2]. We develop a systematic method for representing active-band subspaces containing topological flat bands in terms of compact molecular orbitals, and show that the effective models describing such active-band subspaces take the form of the Anderson lattice model. Due to the dissimilar bandwidth between the flat and dispersive bands, orbital-selective Mott correlations develop over a broad range of parameters, which, in turn, drive a quantum phase transition between a Fermi liquid with a large Fermi surface and an itinerant magnet with a small Fermi surface. Strange-metallic behaviors emerge in the regime associated with the quantum critical point (QCP). Implications for the emergence of unconventional superconductivity and the phase diagram will be discussed.

References:

1. L. Ye et al., Nat. Phys. 20, 610 (2024); S. A. Ekahana, Nature 627, 67 (2024); L. Liu et al., Nature 632, 1032 (2024); J. Huang et al., Nat. Phys. 20, 603 (2024); J. Huang et al., npj, Quantum Materials 9, 71 (2024).

2. L. Chen et al., Nat. Commun. 15, 5242 (2024); L. Chen et al., arXiv:2307.09431; F. Xie et al., arXiv 2403.03911 (2024); H. Hu et al., Sci. Adv. 9, eadg0028 (2023).

Acknowledgement: Work done in collaboration with Lei Chen, Fang Xie, Haoyu Hu, Jennifer Cano, Ying Li, Yuefei Huang, Chadan Setty, Boris Yakobson, Roser Valenti, and Qimiao Si.