Localization effects in the disordered Ta interlayer of multilayer Ta-FeNi films: Evidence from dc transport and spectroscopic ellipsometry study

TL;DR

This study investigates how increasing the thickness of disordered Ta interlayers in multilayer Ta-FeNi films affects electron localization, revealing a transition towards localized electron states through dc transport and spectroscopic ellipsometry.

Contribution

It provides new insights into the localization effects in disordered metallic interlayers using combined dc transport and spectroscopic ellipsometry techniques.

Findings

Increased Ta layer thickness enhances electron localization.

Drude response decreases with thicker Ta layers.

Conductivity drops below the weak localization limit for thicker layers.

Abstract

Using dc transport and wide-band spectroscopic ellipsometry techniques, we study localization effects in the disordered metallic Ta interlayer of different thickness in the multilayer films (MLFs) (Ta - FeNi)_N grown by rf sputtering deposition. In the grown MLFs, the FeNi layer was 0.52 nm thick, while the Ta layer thickness varied between 1.2 and 4.6 nm. The Ta layer dielectric function was extracted from the Drude-Lorentz simulation. The dc transport study of the MLFs implies non-metallic (dr/dT<0) behavior, with negative temperature coefficient of resistivity (TCR). The TCR absolute value increases upon increasing the Ta interlayer thickness, indicating enhanced electron localization. With that, the free charge carrier Drude response decreases. Moreover, the pronounced changes occur at the extended spectral range, involving the higher-energy Lorentz bands. The Drude dc conductivity drops below the weak localization limit for the thick Ta layer. The global band structure reconstruction may indicate the formation of a nearly localized many-body electron state.