Field-Tuned Quantum Critical Point in CeCoIn$_5$ Near the Superconducting Upper Critical Field

TL;DR

This study reveals a magnetic field tuned quantum critical point near the superconducting upper critical field in CeCoIn$_5$, with anisotropic effects indicating robust quantum fluctuations and a close relationship between quantum criticality and superconductivity.

Contribution

It provides the first systematic analysis of high-field specific heat and resistivity in CeCoIn$_5$, demonstrating the existence of a field-tuned quantum critical point near H_{c2} for different orientations.

Findings

Quantum critical point exists near H_{c2} despite anisotropy.

Fermi liquid recovery is more gradual with in-plane magnetic field.

Quantum fluctuations are robust against magnetic field variations.

Abstract

We report a systematic study of high magnetic field specific heat and resistivity in single crystals of CeCoIn_5 for the field oriented in the basal plane (H//ab) of this tetragonal heavy fermion superconductor. We observe a divergent electronic specific heat as well as an enhanced A coefficient of the T^{2} law in resistivity at the lowest temperatures, as the field approaches the upper critical field of the superconducting transition. Together with the results for field along the tetragonal axis (H//c), the emergent picture is that of a magnetic field tuned quantum critical point which exists in the vicinity of the superconducting H_{c2} despite a variation of a factor of 2.4 in H_{c2} for different field orientations. This suggests an underlying physical reason exists for the superconducting H_{c2} to coincide with the quantum critical field. Moreover, we show that the recovery of a Fermi Liquid ground state with increasing magnetic field is more gradual, meaning that the fluctuations responsible for the observed quantum critical phenomena are more robust with respect to magnetic field, when the magnetic field is applied in-plane. Together with the close proximity of the quantum critical point and H_{c2} in CeCoIn_5 for both field orientation, the anisotropy in the recovery of the Fermi liquid state might constitute an important piece of information in identifying the nature of the fluctuations that become critical.