Optical Properties of TiN Thin Films close to the Superconductor-Insulator Transition

TL;DR

This study investigates the optical properties of TiN thin films near the superconductor-insulator transition, revealing features similar to high-temperature superconductors and providing insights into their electronic excitations.

Contribution

It provides a detailed analysis of the optical conductivity of TiN films, identifying metallic and excitation contributions, and draws parallels with high-temperature superconductor behavior.

Findings

Identification of metallic and finite energy excitations in TiN.

Observation of a mid-infrared feature reminiscent of a pseudogap.

Spectral weight analysis of optical conductivity.

Abstract

We present the intrinsic optical properties over a broad spectral range of TiN thin films deposited on a Si/SiO$_2$ substrate. We analyze the measured reflectivity spectra of the film-substrate multilayer structure within a well-establish procedure based on the Fresnel equation and extract the real part of the optical conductivity of TiN. We identify the metallic contribution as well as the finite energy excitations and disentangle the spectral weight distribution among them. The absorption spectrum of TiN bears some similarities with the electrodynamic response observed in the normal state of the high-temperature superconductors. Particularly, a mid-infrared feature in the optical conductivity is quite reminiscent of a pseudogap-like excitation.