Loss of Quasiparticles: From Strange Metals to Flat Bands

Strange metals are a form of correlated systems at extreme, and a loss of Landau quasiparticles represents an underlying cause for their properties. It is in contrast to the resiliency of the quasiparticles when the electron-electron interactions are treated perturbatively. One prototype setting of interest arises in heavy fermion strange metals, which are well described by the beyond-Landau quantum criticality of Kondo destruction [1,2]. This mechanism has been supported by a large body of experiments, and the predicted loss of quasiparticles has recently received fairly direct evidence from shot noise [3]. Surprisingly, quantum information approaches in the form of entanglement witnesses have been found to elucidate the quantum critical fluid and loss of quasiparticles [4]. As another exemplary platform, I will consider the emergent flat bands of d-electron systems with a kagome or related frustrated lattice [5]. The notion of compact molecular orbitals is introduced, leading to a Kondo lattice description. This allows us [5] to advance the first theoretical understanding of the observed strange metal behavior, and to predict a phase diagram that is now seen in a new kagome metal. From this framework, I will briefly address the recently observed superconductivity in twisted WSe2 [6]. Some general implications will be discussed.

[1] H. Hu, L. Chen & Q. Si, Nat Phys, in press (2024); Q. Si et al., Nature 413, 804 (2001).

[2] S. Paschen & Q. Si, Nat. Rev. Phys. 3, 9 (2021); S. Kirchner et al, Rev. Mod. Phys. 92, 011002 (2020).

[3] L. Y. Chen et al., Science 382, 907 (2023); Y. Wang et al., Phys. Rev. Research 6, L042045 (2024).

[4] Y. Fang et al., arXiv:2402.18552.

[5] L. Chen et al., arXiv:2307.09431; F. Xie et al., arXiv 2403.03911 (2024); L. Chen et al., Nat Comm 15, 5242 (2024); H. Hu & Q. Si, Sci. Adv. 9, eadg0028 (2023).

[6] F. Xie et al., arXiv:2408.10185.