Anomalous response of superconducting titanium nitride resonators to terahertz radiation

TL;DR

This study investigates the unusual behavior of titanium nitride superconducting resonators under terahertz radiation, revealing responses that differ from theoretical expectations and other materials, likely due to inhomogeneous superconducting states.

Contribution

The paper provides the first experimental analysis of TiN KIDs' response to terahertz radiation, highlighting anomalous responsivity and noise behavior linked to inhomogeneous superconductivity.

Findings

Responsivity increases with radiation power, contrary to expectations.

Noise remains unaffected by radiation power levels.

NEP improves with higher radiation powers, opposite to other KID types.

Abstract

We present an experimental study of KIDs fabricated of atomic layer deposited TiN films, and characterized at radiation frequencies of $350$~GHz. The responsivity to radiation is measured and found to increase with increasing radiation powers, opposite to what is expected from theory and observed for hybrid niobium titanium nitride / aluminium (NbTiN/Al) and all-aluminium (all-Al) KIDs. The noise is found to be independent of the level of the radiation power. The noise equivalent power (NEP) improves with higher radiation powers, also opposite to what is observed and well understood for hybrid NbTiN/Al and all-Al KIDs. We suggest that an inhomogeneous state of these disordered superconductors should be used to explain these observations.