Quantum-critical phase out of frustrated magnetism in a strongly correlated metal

TL;DR

This paper reports the discovery of a quantum-critical phase in a frustrated magnet, revealing a new state of matter that transitions into a Fermi liquid via a Mott-like crossover, with implications for unconventional superconductivity.

Contribution

It demonstrates the emergence of a paramagnetic quantum-critical phase due to magnetic frustration in a strongly correlated metal, linking it to electron localization-delocalization transitions.

Findings

Identification of a quantum-critical phase in CePdAl due to magnetic frustration.

Observation of a Mott-like crossover to a Fermi liquid.

Mapping of a phase diagram with pressure and magnetic field showing electron localization transitions.

Abstract

Strange-metal phenomena often develop at the border of antiferromagnetic order in strongly correlated metals. It has been well established that they can originate from the fluctuations anchored by the point of continuous quantum phase transition out of the antiferromagnetic order, i.e., a quantum critical point. What has been unclear is how these phenomena can be associated with a potential new phase of matter at zero temperature. Here we show that magnetic frustration of the 4f-local moments in the distorted Kagome intermetallic compound CePdAl gives rise to such a paramagnetic quantum-critical phase. Moreover, we demonstrate that this phase turns into a Fermi liquid through a Mott-like crossover; in a two-dimensional parameter space of pressure and magnetic field, this crossover is linked to a line of zero-temperature 4f-electron localization-delocalization phase transitions at low and moderate pressures. Our discovery motivates a new design principle for strongly correlated metallic states with unconventional excitations that may underlie the development of such effects as high temperature superconductivity.