paper

Bipartite Fluctuations of Critical Fermi Surfaces

arXiv:2404.04331 · doi:10.1103/dflw-rksw

Abstract

Fluctuations of conserved quantities within a subsystem are non-local observables that provide unique insights into quantum many-body systems. In this paper, we study bipartite charge (and spin) fluctuations across interaction-driven ``metal-insulator transitions'' out of Landau Fermi liquids. The ``charge insulators'' include a class of non-Fermi-liquid states of fractionalized degrees of freedom, such as compressible composite Fermi liquids (for spinless electrons) and incompressible spin-liquid Mott insulators (for spin- electrons). We find that charge fluctuations exhibit distinct leading-order scalings across the transition: in Landau Fermi liquids and in charge insulators, where is the linear size of the subsystem. In composite Fermi liquids, under certain conditions, we also identify a universal constant term when the subsystem geometry contains a sharp corner, where denotes a function of the corner angle, and is the Hall conductivity. At the critical point, provided the transition is continuous, the leading scaling is accompanied by a subleading universal corner contribution with the same angle dependence , and the universal coefficient is directly related to the predicted universal jumps in longitudinal and Hall resistivities. These results establish fluctuation-transport relations, paving the way for numerical and experimental studies of unconventional quantum criticalities in metals.

30 pages, 4 figures; updated discussion on charge insulators; accepted version

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