Evidence for a delocalization quantum phase transition without symmetry breaking in CeCoIn<sub>5</sub>.

Maksimovic, Nikola; Eilbott, Daniel H; Cookmeyer, Tessa; Wan, Fanghui; Rusz, Jan; Nagarajan, Vikram; Haley, Shannon C; Maniv, Eran et al. · Science · 2022

basic_science · Level V

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Abstract

The study of quantum phase transitions that are not clearly associated with broken symmetry is a major effort in condensed matter physics, particularly in regard to the problem of high-temperature superconductivity, for which such transitions are thought to underlie the mechanism of superconductivity itself. Here we argue that the putative quantum critical point in the prototypical unconventional superconductor CeCoIn<sub>5</sub> is characterized by the delocalization of electrons in a transition that connects two Fermi surfaces of different volumes, with no apparent broken symmetry. Drawing on established theory of f-electron metals, we discuss an interpretation for such a transition that involves the fractionalization of spin and charge, a model that effectively describes the anomalous transport behavior we measured for the Hall effect.