Thermodynamic properties of nodal superconductors close to a magnetic quantum critical point

TL;DR

This paper investigates how magnetic quantum criticality affects thermodynamic properties of multiband unconventional superconductors, revealing nonmonotonic behavior in penetration depth and specific heat near the critical point, supported by experimental data.

Contribution

It introduces a theoretical model linking magnetic quantum fluctuations to thermodynamic signatures in nodal superconductors near a quantum critical point, validated by experimental comparison.

Findings

Quantum fluctuations cause nonmonotonic penetration depth dependence on doping.

Magnetic fluctuations contribute significantly to specific heat at the coexistence phase.

Theoretical results align with experimental thermodynamic measurements in BaFe₂(As₁₋ₓPₓ)₂.

Abstract

In this work we study thermodynamic manifestations of the quantum criticality in multiband unconventional superconductors. As a guiding example we consider the scenario of magnetic quantum critical point in the model that captures superconductivity coexistence with the spin-density wave. We show that in situations when the superconducting order parameter has incidental nodes at isolated points, quantum magnetic fluctuations lead to the renormalization of the relative $T$-linear slope of the London penetration depth. This leads to the nonmonotonic dependence of the penetration depth as a function of doping and the concomitant peak structure across the quantum critical point. In addition, we determine contribution of magnetic fluctuations to the specific heat at the onset of the coexistence phase. Our theoretical analysis is corroborated by making a comparison of our results with the recent experimental data from the low-temperature thermodynamic measurements at optimal composition in BaFe$_2$(As$_{1-x}$P$_x$)$_2$.