The high-T _c superconducting (HTS) bicrystal YBa ₂ Cu ₃ O _7-δ (YBCO) zero-bias-operation Josephson junction (JJ) harmonic mixer coupled with a bowtie loaded meander antenna (BLMA) is proposed and studied at 0.21 THz. When the JJ mixer coupled with the BLMA, the maximal harmonic number increases up to 146 with the conversion efficiency of -63.6 dB at the bath temperature around 4.6 K compared to a mixer coupled with a log-periodic antenna (LPA) of only a maximal harmonic number of 46 with the conversion efficiency of -71.6 dB. The mixer coupled with the BLMA has a higher order harmonic mixing with a lower local oscillator (LO) power of 1.26 dBm, which further illustrates its superiority to that coupled with a LPA with the LO power of 5.59 dBm. The experiment verifies the merits of the JJ harmonic mixer operating at zero bias as a promising device in terahertz regions.

Josephson devices have demonstrated the capability to work as harmonic mixers at terahertz frequencies. Low temperature devices, in particular Nb–Nb point contacts have proven particularly successful. However, practical applications of these devices have been limited by the need of utilizing liquid helium. To overcome this limitation we have investigated the use of high- T _c devices. In this paper, we report mixings up to the 154th harmonic at zero-bias in a series of YBa ₂ Cu ₃ O _7−δ (YBCO) grain boundary Josephson junctions. We have integrated a meander series of three bicrystal YBCO Josephson junctions with a log-periodic antenna. When properly operated, this configuration allows to reach a harmonic number much higher than what possible with a single junction. This shows that the mixing performance benefits from the synchronous operation which also results in an improvement of dynamic range. We believe that the integration of a higher number of phase-locked junctions may further improve the mixer’s performance. Future studies should investigate the effect of higher number of junctions on the mixer performances, as well as the effect of the meander length.

Few-layer transition metal disulfides have attracted much attention in the field of optoelectronic devices due to their unique optical and electronic properties. Among them, two-dimensional tantalum diselenide (TaSe ₂ ) nanocrystals have excellent flexibility, fast optical response properties, outstanding chemical stability, and light absorption properties and thus have potential applications in the field of optical sensors. Here we present for the first time an optical biosensor based on multilayer 2H-phase TaSe ₂ /graphene, which can respond to subtle refractive index changes of the sensing medium by precise tuning of the optical and structural parameters of the sensor. The results of theoretical scientific studies show that multilayer TaSe ₂ /graphene films at the nano-scale can produce extremely strong long-range surface plasmon resonance (LRSPR) in the sensor structure proposed in this paper. Compared with the conventional Au nanofilm surface plasmon resonance (SPR) sensor, the figure of merit (fOm) of the proposed TaSe ₂ SPR-based sensor improved by a factor of 9.6. Our theoretical study demonstrates that TaSe ₂ is a surface plasmonic material with excellent performance and provides a theoretical reference for its experimental study in the field of biosensors.

MXenes-based van der Waals heterojunction materials with excellent chemical stability and bioaffinity have been widely used in biosensing in recent years. We propose a new MoSe ₂ @Zr ₂ CO ₂ heterostructure as a long-range surface plasmon resonance (LRSPR) sensor based on the Kretschmann configuration from simulation and optimize the structure parameters algorithmically. Firstly, we investigate the effect of different layers of MoSe ₂ @Zr ₂ CO ₂ heterojunction on the LRSPR wave. The results show that the optimal number of layers for heterogeneous layers is 18. Secondly, the effects of dielectric thickness and refractive index on sensitivity are investigated in depth, and optimized structural parameters are obtained. Finally, the effect of prisms with different refractive coefficients on the sensor performance is also discussed, and it is shown that prisms with lower refractive coefficients can effectively improve the sensitivity performance of the sensor. The sensor response performance to biomolecules is greatly enhanced due to the gain of light absorption and surface plasmon resonance. Compared with the conventional precious metal Au-based (50 nm) thin-film SPR sensor, the figure of merit (FOM) of the sensor is improved by a factor of 8.16, and higher sensitivity (92.48°/RIU) and quality factor (319.63 RIU ^-1 ) are obtained in the visible range.

In a quasi-optical system, the high temperature superconducting terahertz detector often suffers from a fundamental problem of low coupling efficiency with the terahertz signal, especially for the detector based on YBa₂Cu₃O_7-δ (YBCO) bicrystal Josephson junction (JJ) due to a small normal-state resistance. Here, we developed a bowtie loaded meander antenna to enhance coupling efficiency. Differing from the conventional characterization confining on vector network analyzers, we applied three methods to evaluate the antenna, including the measurements of the maximal size of the first order Shapiro step under per incident power, the coupling efficiency between the antenna and the junction, and voltage responsivity. Furthermore, with simulation analysis, we propose that the inductive reactance of the YBCO bicrystal JJ is around 60 ohms under terahertz irradiation at 210 GHz, thus, the reactance is comparable as that of the antenna.