Dresden 2026 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 5: Superconductivity: Sample Preparation and Characterization
TT 5.2: Talk
Monday, March 9, 2026, 09:45–10:00, CHE/0089
Gap smearing and sub-gap states in disordered nitride superconductors — •Frederik Bolle1, Yayi Lin1, Heidemarie Krüger2, Martin Dressel1, and Marc Scheffler1 — 11. Physikalisches Institut, Universität Stuttgart — 2Leibniz IPHT, Jena
In recent years nitride-based superconductors have gathered a lot of attention due to their high critical temperatures, large kinetic inductances, and ease of manufacturing.
According to the BCS theory, at temperatures far below the critical transition temperature, the superconducting s-wave state is characterized by a hard gap Δ and a coherence peak above the gap. In the case of substantial disorder, subgap states emerge and the coherence peak is suppressed.
We present the quasiparticle dynamics of ultra-thin NbN and MoN films with various levels of disorder, probed at energies comparable to the energy gap using THz spectroscopy (0.2 meV−10 meV). To quantify the additional pair-breaking we employ the phenomenological Dynes model for the optical conductivity.
We find in the case of NbN, a temperature-independent pair-breaking rate, which suggests magnetic impurities, while MoN shows a strongly temperature-dependent pair-breaking rate, which we attribute to inhomogeneities of the local gap function.
The understanding of this excess quasiparticle density plays an important role for decoherence and loss mechanisms in quantum circuits at millikelvin temperatures.
Keywords: Supercondcuting thin films; THz spectroscopy; Disordered superconductors; Superconducting density of states; Nitride superconductors