Electrical resistance measurement under high pressure is one of the essential experiments for measuring electronic properties under pressure, including pressure-induced superconductivity. Several techniques we have developed are indispensable for measurements in the pressure range exceeding 1 million atmospheres. Here, the techniques and procedures, as well as the technical details, are described by showing measurement examples.

The discovery of superconductivity and its novel mechanisms has attracted attention in condensed matter physics. In this article, we review our recent work on pressure-induced superconductivity at the semiconductor-semimetal boundary regions in Ta₂NiSe₅ and LaOPbBiS₃. Ta₂NiSe₅ is known as the promising candidate for excitonic insulator, and our high-pressure experiments have led to the discovery of superconductivity and a phase diagram covering the transition from the semiconducting to the semimetallic regime. We also report on the pressure-induced superconductivity in the bismuth chalcogenide semiconductor LaOPbBiS₃ in the vicinity of the localization threshold.

We show the synthesis methods, crystal structure, physical properties, electronic structure, and atomic vibration characteristics of high-entropy (HE) metal-telluride superconductors. As well known, HE superconductors have been drawing much attention as a new class of disordered superconductors. In metal tellurides, T_c-pinning phenomenon, which is the robustness of T_c to applied pressure, has been observed in HE compositions. The possible causes of the exotic phenomenon are glassy atomic vibrations in the HE metal tellurides.

This study reviews newly discovered high-temperature cuprate superconductors synthesized using high-pressure techniques. These materials feature double CuO₂ planes separated by Sr within their blocking layers, with Sr also serving as the principal element comprising the blocking layers. Previously, CuO₂ planes in cuprate superconductors with critical temperatures (T_c) exceeding 100 K were invariably separated by Ca. Remarkably, some of these new cuprates, such as (Hg,Re)Sr₂SrCu₂O_y, Sr₂SrCu₂O_4+yF_2-y, achieve a T_c in the 100 K range despite the absence of Ca in their chemical composition. This discovery underscores the potential for further exploration of new cuprate superconductors through the application of high-pressure synthesis techniques.

We have learned in elemental thermodynamics that the distinction between the liquid and gas states diminishes as the temperature approaches the critical temperature, T_c. At T = T_c, the volumes of the liquid and gas states are coincident, defining the critical volume V_c. However, the recent studies by Woodcock challenge the reality of the critical volume. By analyzing his series of papers and related papers, the reliability of his studies has been examined, with confirming his results.

Boron-doped diamond (BDD) epitaxial film is a promising material for stable electrodes under extreme conditions. Recently, we successfully developed the BDD electrodes in a sample space of a diamond anvil cell (DAC) for an electrical transport measurement of materials under high pressure. By using this system, various superconducting materials are discovered in the short term. In this article, the details of the fabrication process of the BDD electrodes, the variation of the type of BDD pattern, and several examples of the discovery of superconductors are introduced for future collaborating work with wide research fields.