Direct observation of the superconducting gap in thin film of titanium nitride using terahertz spectroscopy

TL;DR

This study uses terahertz spectroscopy to directly observe the superconducting energy gap and charge carrier dynamics in a thin film of titanium nitride, confirming conventional BCS superconductivity.

Contribution

It provides the first direct measurement of the superconducting gap in TiN thin films using terahertz spectroscopy, and analyzes charge carrier dynamics in detail.

Findings

Superconducting gap directly observed at terahertz frequencies.

Superconductivity in TiN consistent with BCS theory.

Normal state properties align with conventional superconductors.

Abstract

We report on the charge carrier dynamics of superconducting titanium nitride (TiN) in the frequency range 90 - 510 GHz (3 - 17 cm-1). The experiments were perfomed on a 18 nm thick TiN film with a critical temperature of 3.4 K. Measurements were carried out from room temperature down to 2 K, and in magnetic fields up to 7 T. We extract the real and imaginary parts of the complex conductivity as a function of frequency and temperature, directly providing the superconducting energy gap. Further analysis yields the superconducting London penetration depth. The findings as well as the normal state properties strongly suggest conventional BCS superconductivity, underlined by the BCS ratio 3.44. Detailed analysis of the charge carrier dynamics of the silicon substrate is also discussed.