On-chip time-domain terahertz spectroscopy of superconducting films below the diffraction limit

• Published in: arXiv.org
• Main Authors: Potts, Alex, Nayak, Abhay, Nagel, Michael, Kelson Kaj, Stamenic, Biljana, John, Demis D, Averitt, Richard D, Young, Andrea F
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 10.02.2023
• Subjects: Condensed matter physics; Diffraction; Heterostructures; Physics - Superconductivity; Spectroscopy; Superconducting films; Superconductivity; Switches; Time domain analysis
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2302.05434

Free-space time domain THz spectroscopy accesses electrodynamic responses in a frequency regime ideally matched to interacting condensed matter systems. However, THz spectroscopy is challenging when samples are physically smaller than the diffraction limit of ~0.5 mm, as is typical, for example, in van der Waals materials and heterostructures. Here, we present an on-chip, time-domain THz spectrometer based on semiconducting photoconductive switches with a bandwidth of 200 GHz to 750 GHz. We measure the optical conductivity of a 7.5-\(\mu\)m wide NbN film across the superconducting transition, demonstrating spectroscopic signatures of the superconducting gap in a sample smaller than 2% of the Rayleigh diffraction limit. Our spectrometer features an interchangeable sample architecture, making it ideal for probing superconductivity, magnetism, and charge order in strongly correlated van der Waals materials.