Identification of a Marginal Fermi-Liquid in Itinerant Ferromagnet CoS2

TL;DR

This paper presents experimental evidence that CoS2 exhibits marginal Fermi-liquid behavior, with a phase diagram featuring a tricritical point, and demonstrates how magnetic fields can tune the system between marginal and conventional Fermi-liquid states.

Contribution

It provides the first comprehensive experimental validation of marginal Fermi-liquid behavior in an itinerant ferromagnet and explores the effects of magnetic fields on spin fluctuations.

Findings

CoS2 shows marginal Fermi-liquid characteristics in specific heat, resistivity, and susceptibility.

A tricritical point exists in the phase diagram, enabling precise testing of spin fluctuation theory.

Magnetic fields suppress spin fluctuations and restore conventional Fermi-liquid behavior.

Abstract

We report specific heat, resistivity and susceptibility measurements at different temperatures, magnetic fields, and pressures to provide solid evidence of CoS2 being a marginal Fermi liquid. The presence of a tricritical point in the phase diagram of the system provides an opportunity to test the spin fluctuation theory with a high limit of accuracy. A magnetic field suppresses the amplitude of the spin fluctuations and recovers conventional Fermi liquid behavior, connecting both states continuously.