Effect of magnetic criticality and Fermi-surface topology on the magnetic penetration depth

TL;DR

This paper studies how anti-ferromagnetic quantum criticality influences the magnetic penetration depth in line-nodal superconductors, revealing enhanced zero-temperature values and unusual temperature dependence consistent with experiments.

Contribution

It demonstrates the impact of AF quantum criticality on $ ext{lambda}(T)$ and highlights the Fermi-surface topology's role, providing a new way to detect quantum critical points.

Findings

Zero-temperature penetration depth $ ext{lambda}(0)$ is significantly enhanced near AF criticality.

Temperature dependence of $ ext{lambda}(T)$ deviates from linearity, approaching $T^{1.5}$ behavior.

Results align with experimental observations in cuprates, iron pnictides, and heavy-fermion superconductors.

Abstract

We investigate the effect of anti-ferromagnetic (AF) quantum criticality on the magnetic penetration depth $\lambda(T)$ in line-nodal superconductors, including the cuprates, the iron pnictides, and the heavy-fermion superconductors. The critical magnetic fluctuation renormalizes the current vertex and drastically enhances zero-temperature penetration depth $\lambda(0)$, which is more remarkable in the iron-pnictide case due to the Fermi-surface topology. Additional temperature ($T$) dependence of the current renormalization makes the expected $T$-linear behavior at low temperatures approaching to $T^{1.5}$ asymptotically. These anomalous behaviors are well consistent with experimental observations. We stress that $\lambda(T)$ is a good probe to detect the AF quantum critical point in the superconducting state.