STAGE Plasmonic structures with High Tc Superconductors for a new generation of THz devices

The THz region of the electromagnetic spectrum, which may be defined as covering the range from 0.3 to 10 THz is a frontier area for research in many fields, including physics, astronomy, chemistry, material science, communication, biology and medicine. Indeed, THz radiation can propagate through light materials and
within the atmosphere for specific frequency windows, enabling imaging at a distance in situations where regular optical systems cannot, that is through fog, tissues, clothes, walls. Since their frequency is very high, THz waves can be used for large data rate communications. Moreover, since most materials have specific rotational or vibrational modes in this wavelength region, spectroscopy-using THz is a powerful tool to identify substances, such as pollutants, chemicals, explosives, odd biological samples. Combined with the capability to "see through", it is possible to make "hyper-spectral" imaging of a hidden scene. However, despite the tremendous array of possible applications, the THz region of the electromagnetic spectrum has, so far, not been exploited fully due to the limited number of suitable sources and detectors. Although a wide range of technologies has recently begun to fill the THz gap, there are still needs of high sensitivity and high resolution detectors, with low power consumption, that can be fitted in a small volume. Current THz technology is mainly based on III-V semiconductors, with two important components: Quantum Cascade Lasers (QCLs) as coherent sources, and detectors based on Quantum Wells (QWs). To enhance their performances, metallic waveguides and micro-cavities are widely used to confine the electromagnetic field in some region of the device, thanks to the so-called “plasmonic effects. To increase their performances even further, we propose to replace the metallic parts by High Tc superconducting (HTc) ones. First, we may reduce losses because the dissipation is low in the superconducting state, and second, and more importantly, we can tune the frequency resonance of the
cavities, which are essentially LC resonators. Indeed, in addition to the geometrical inductance, superconductors have a “kinetic inductance”, that varies with temperature. Another tuning possibility is to insert in the structure "Josephson junctions (JJ) and “SQUIDs”, which are superconducting devices whose
inductance varies with a small magnetic field. We have shown that such devices operate in the lower part of the THz range.