A peak in the critical current for quantum critical superconductors

Soon-Gil Jung,Han-Oh Lee,Sangyun Lee,Tuson Park,Soonbeom Seo,Eric D Bauer

doi:10.1038/s41467-018-02899-5

Abstract

Generally, studies of the critical current Ic are necessary if superconductors are to be of practical use, because Ic sets the current limit below which there is a zero-resistance state. Here, we report a peak in the pressure dependence of the zero-field Ic, Ic(0), at a hidden quantum critical point (QCP), where a continuous antiferromagnetic transition temperature is suppressed by pressure toward 0 K in CeRhIn5 and 4.4% Sn-doped CeRhIn5. The Ic(0)s of these Ce-based compounds under pressure exhibit a universal temperature dependence, underlining that the peak in zero-field Ic(P) is determined predominantly by critical fluctuations associated with the hidden QCP. The dc conductivity σdc is a minimum at the QCP, showing anti-correlation with Ic(0). These discoveries demonstrate that a quantum critical point hidden inside the superconducting phase in strongly correlated materials can be exposed by the zero-field Ic, therefore providing a direct link between a QCP and unconventional superconductivity.

Highlights

Unconventional superconductivity (SC) often is observed in close proximity to a magnetically ordered phase, where the SC transition temperature Tc forms a dome against a non-thermal control parameter, such as the external pressure, chemical substitution, or magnetic field[1,2,3,4,5,6]
At an optimal value of the tuning parameter, where Tc is the highest, normal state properties do not follow predictions for Landau–Fermi liquids: the electrical resistivity (ρ) does not exhibit a T2 dependence, and the electronic specific heat coefficient (γ = C/T) does not saturate, but rather diverges with decreasing temperature[1, 2, 7]. These nonFermi liquid (NFL) behaviors arise from incoherent critical fluctuations associated with a quantum critical point (QCP) hidden inside the SC dome of heavy fermion compounds and some Fe-based superconductors, such as BaFe2(As1 −xPx)[21, 2, 4, 6, 8]
Normalized values of Ic(T, P) follow a common universal curve for each material, suggesting an intrinsic, fundamental connection to quantum criticality. Supporting this conclusion, the magnetic field dependence of the flux-pinning force (Fp = Ic × μ0H), normalized to its maximum value, forms a pressure-invariant universal curve for each compound. These discoveries demonstrate that the pressure evolution of zero-field Ic is determined mainly by quantum critical fluctuations, and that the peak in Ic is a direct link to the hidden QCP

Summary

Introduction

Unconventional superconductivity (SC) often is observed in close proximity to a magnetically ordered phase, where the SC transition temperature Tc forms a dome against a non-thermal control parameter, such as the external pressure, chemical substitution, or magnetic field[1,2,3,4,5,6]. The zero-field critical current density Jc (equal to Ic/A, where A is the sample cross sectional area perpendicular to current) of the hole-doped highTc cuprate superconductor Y0.8Ca0.2Ba2Cu3Oy has a sharp peak that is centered on a critical hole-doping where the pseudogap boundary line projects to zero temperature, and that is attributed in model calculations to changes in the superfluid density[12, 13] These results indicate that Ic measurements may provide an opportunity to explore the relationship between unconventional SC and any QCP that is hidden beneath the SC dome. These discoveries demonstrate that the pressure evolution of zero-field Ic is determined mainly by quantum critical fluctuations, and that the peak in Ic is a direct link to the hidden QCP

Methods

Results

Conclusion