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Photoconductive antennas made on low-temperature-grown Be doped InxGa1−xAs (0.45⩽x⩽0.53) have been investigated focusing on the terahertz emission properties. In the antenna of x=0.45, the resistance as high as 3MΩ enabled us to increase the bias field up to 60kV∕cm, and the terahertz waves emitted from the antenna were significantly enhanced. In addition, terahertz waves with the spectral range over 2.5THz and the peak to noise ratio of 45dB were generated and detected using only 1.56μm pulses.

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High-entropy alloys (HEAs) are a new class of materials which are being energetically studied around the world. HEAs are characterized by a multicomponent alloy in which five or more elements randomly occupy a crystallographic site. The conventional HEA concept has developed into simple crystal structures such as face-centered-cubic (fcc), body-centered-cubic (bcc) and hexagonal-closed packing (hcp) structures. The highly atomic-disordered state produces many superior mechanical or thermal properties. Superconductivity has been one of the topics of focus in the field of HEAs since the discovery of the bcc HEA superconductor in 2014. A characteristic of superconductivity is robustness against atomic disorder or extremely high pressure. The materials research on HEA superconductors has just begun, and there are open possibilities for unexpectedly finding new phenomena. The present review updates the research status of HEA superconductors. We survey bcc and hcp HEA superconductors and discuss the simple material design. The concept of HEA is extended to materials possessing multiple crystallographic sites; thus, we also introduce multisite HEA superconductors with the CsCl-type, α-Mn-type, A15, NaCl-type, σ-phase and layered structures and discuss the materials research on multisite HEA superconductors. Finally, we present the new perspectives of eutectic HEA superconductors and gum metal HEA superconductors.

We have developed embedded thin-film micro-strip-line-based sensor chips working in terahertz regime. In the chip, terahertz waves are generated and detected with femtosecond optical pulses accessed from the back side of the chips. Moreover, the spectroscopic sensitivity can be freely adjusted by changing the thickness of a polyimide cover layer. They make it easy to measure polar liquids. The measurement of water is demonstrated with spectral range from 30GHzto1–1.5THz, where the upper limit depends on the thickness of the cover layer.