Regensburg 2025 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 5: Superconductivity: Properties and Electronic Structure I
TT 5.6: Vortrag
Montag, 17. März 2025, 10:45–11:00, H36
THz response of ultra thin NbN films grown by atomic layer deposition — •Frederik Bolle1, Yayi Lin1, Heidemarie Schmidt2, Martin Dressel1, and Marc Scheffler1 — 11. Physikalisches Institut, Universität Stuttgart — 2Leibniz IPHT, Jena
Most elementary excitations and collective modes of superconductors lie in the THz frequency range, making THz spectroscopy an ideal tool to directly measure the superconducting energy gap and superfluid density. By combining the spectral ranges from continuous, coherent backward wave oscillators and time-domain methods we can investigate a broad frequency range from 1.6 cm−1 (0.2 meV) up to 100 cm−1 (12.4 meV). We characterize the superconducting state of grown NbN films in particular concerning the behavior of its energy scales as the film becomes increasingly two dimensional approaching the superconductor insulator transition (SIT). We investigate films with thickness ranging from 4.5 nm and 20 nm and find a continuous suppression of the superconducting energy gap and superfluid density with reduced film thickness. These results enable a quantitative device design for various applications of NbN thin films such as high kinetic inductance circuitry.
Keywords: Thin-films; Quasi optical spectroscopy; Terahertz-Time-Domain spectroscopy; Low temperatures; Disordered superconductors