Infrared Vortex-State Electrodynamics in Type-II Superconducting Thin Films

TL;DR

This study investigates how magnetic fields affect the electrodynamics of type-II superconducting thin films using infrared spectroscopy, revealing vortex-induced pair-breaking effects and modeling the vortex state as an effective medium.

Contribution

It provides a detailed infrared spectroscopic analysis of vortex-state electrodynamics in NbTiN and NbN thin films, applying Maxwell-Garnett theory to explain spectral features and uncover pair-breaking effects.

Findings

Superconducting signatures are reduced under magnetic fields.

Vortex state modeled as a two-component effective medium.

Magnetic-field-induced pair-breaking effects are observed.

Abstract

The vortex-state electrodynamics of s-wave superconductors has been studied by infrared spectroscopy. Far-infrared transmission and reflection spectra of superconducting NbTiN and NbN thin films were measured in a magnetic field perpendicular to the film surface, and the optical conductivity was extracted. The data show clear reduction of superconducting signature. We consider the vortex state as a two-component effective medium of normal cores embedded in a BCS superconductor. The spectral features are well explained by the Maxwell-Garnett theory. Our analysis supports the presence of magnetic-field-induced pair-breaking effects in the superconducting component outside of the vortex cores.