Magnetic field dependent specific heat and enhanced Wilson ratio in strongly correlated layered cobalt oxide

TL;DR

This study explores how magnetic fields influence the specific heat and electronic properties of a layered cobalt oxide, revealing evidence of a magnetic quantum critical point and enhanced ferromagnetic fluctuations.

Contribution

It provides new insights into the magnetic field dependence of specific heat and Wilson ratio near a quantum critical point in a strongly correlated cobalt oxide.

Findings

Specific heat coefficient decreases near the critical magnetic field.

Enhanced Wilson ratio indicates strong ferromagnetic fluctuations.

High field Wilson ratio approaches the universal Fermi liquid limit.

Abstract

We have investigated the low temperature specific heat properties as a function of magnetic field in the strongly correlated layered cobalt oxide [BiBa$_{0.66}$K$_{0.36}$O$_2$]CoO$_2$. These measurements reveal two kinds of magnetic field dependent contributions in qualitative agreement with the presence of a previously inferred magnetic Quantum Critical Point (QCP). First, the coefficient of the low temperature T$^3$ behavior of the specific heat turns out to sizeably decrease near a magnetic field consistent with the critical value reported in a recent paper. In addition, a moderate but significant enhancement of the Sommerfeld coefficient is found in the vicinity of the QCP suggesting a slight increase of the electronic effective mass. This result contrasts with the divergent behavior of the previously reported Pauli susceptibility. Thus, a strongly enhanced Wilson ratio is deduced, suggesting efficient ferromagnetic fluctuations in the Fermi liquid regime which could explain the unusual magnetic field dependent specific heat. As a strong check, the high magnetic field Wilson ratio asymptotically recovers the universal limit of the local Fermi liquid against ferromagnetism.