On-Chip Time-Domain Terahertz Spectroscopy of Superconducting Films below the Diffraction Limit

Abstract

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 to 750 GHz. We measure the optical conductivity of a 7.5-μm 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.

Room-Temperature Plasmon-Assisted Resonant THz Detection in Single-Layer Graphene Transistors

“…Terahertz (THz) radiation (0.1–10 THz) has a strong perspective in a wide range of different applications, including metrology and characterization of nanomaterials, upcoming 6G wireless communications, noninvasive imaging, biosensing, high-resolution spectroscopy, together with many others. , An emerging and important research area within THz technology is the study of novel, efficient, and functional photodetectors operating at these frequencies . The majority of photodetectors reported to date (if not all), including sensors made of many different nanomaterials, − operate either in broadband mode (i.e., without being selective to a given frequency) at room temperature or over narrow fixed frequency bands (i.e., without being frequency tunable), for example, by embedding antennas in the detector.…”

Fundamental Limits of Few-Layer NbSe2 Microbolometers at Terahertz Frequencies

“…Layered van der Waals (vdW) superconductors have recently emerged as a convenient platform for investigating quantum phenomena arising in two dimensions and for future technology prototypes. − Among them, two-dimensional (2D) niobium diselenide (NbSe 2 ) is one of the most extensively studied compounds. − Not only has it enabled the observation of numerous spectacular effects ranging from high-critical-field Ising superconductivity and charged density waves − to unusual continuous paramagnetic-limited superconducting phase transitions and magnetochiral anisotropy, , but it has also given rise to several interesting applications such as superconducting diodes and rectennas . Despite significant progress in understanding the fundamental properties of this material via transport and optical experiments, − little is known about the response of NbSe 2 to terahertz (THz) radiation. − …”