On the T-dependence of the magnetic penetration depth in unconventional superconductors at low temperatures: can it be linear?

TL;DR

This paper argues that the magnetic penetration depth in unconventional superconductors cannot have a strictly linear temperature dependence at low temperatures, based on thermodynamic principles.

Contribution

It provides a thermodynamic argument that challenges the assumption of linear T-dependence in the penetration depth of unconventional superconductors.

Findings

Thermodynamic constraints disallow strictly linear T-dependence.

The argument applies broadly to superconductors with arbitrary pairing symmetry.

Supports reevaluation of experimental interpretations of penetration depth data.

Abstract

We present a thermodynamics argument against a strictly linear temperature dependence of the magnetic penetration depth, which applies to superconductors with arbitrary pairing symmetry at low temperatures.