Candidates for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were searched by the high-throughput first-principles calculation from an inorganic materials database. The synthesized SnBi2Se4 among the target compounds showed a narrow band gap of 354 meV, and a thermal conductivity of ~1 W･K -1 m -1 at ambient pressure. The sample SnBi2Se4 showed a metal-insulator transition at 11.1 GPa, as predicted by a theoretical estimation. Furthermore, the two pressure-induced superconducting transitions were discovered at under 20.2 GPa and 47.3 GPa. The datadriven search is a promising approach to discover new functional materials.

Magnetic refrigeration exploits the magnetocaloric effect, which is the entropy change upon the application and removal of magnetic fields in materials, providing an alternate path for refrigeration other than conventional gas cycles. While intensive research has uncovered a vast number of magnetic materials that exhibit a large magnetocaloric effect, these properties remain unknown for a substantial number of compounds. To explore new functional materials in this unknown space, machine learning is used as a guide for selecting materials that could exhibit a large magnetocaloric effect. By this approach, HoB2 is singled out and synthesized, and its magnetocaloric properties are evaluated, leading to the experimental discovery of a gigantic magnetic entropy change of 40.1 J kg−1 K−1 (0.35 J cm−3 K−1) for a field change of 5 T in the vicinity of a ferromagnetic second-order phase transition with a Curie temperature of 15 K. This is the highest value reported so far, to the best of our knowledge, near the hydrogen liquefaction temperature; thus, HoB2 is a highly suitable material for hydrogen liquefaction and low-temperature magnetic cooling applications.

To investigate the relationship between the pseudogap and superconductivity, we measured both the in-plane (ρ ab ) and out-of-plane (ρ c ) resistivity for oxygen-controlled Bi 2 Sr 2 CaCu 2 O 8+δ single crystals subject to magnetic fields (parallel to the c axis) of up to 17.5 T. The onset temperature for the superconductive fluctuation, T sc f , is determined by the large positive in-plane magnetoresistance (MR) and negative out-of-plane MR observed near T c , whereas the pseudogap opening temperature T * is determined by the semiconductive upturn of the zero-field ρ c . T sc f was found to scale roughly as T c , with a decreasing temperature interval between them upon doping. On the other hand, T * starts out much higher than T sc f but decreases monotonically upon doping; finally, at a heavily overdoped state, it is not observed above T sc f . These results imply that the pseudogap is not a simple precursor of superconductivity, but that further study is needed to determine whether or not T * exists below T sc f in the heavily overdoped state.

Diamond anvil cell using boron-doped metallic diamond electrodes covered with undoped diamond insulating layer have been developed for electrical transport measurements under high pressure. These designed diamonds were grown on a bottom diamond anvil via a nanofabrication process combining microwave plasma-assisted chemical vapor deposition and electron beam lithography. The resistance measurements of high quality FeSe superconducting single crystal under high pressure were successfully demonstrated by just putting the sample and gasket on the bottom diamond anvil directly. The superconducting transition temperature of FeSe single crystal was enhanced up to 43 K by applying uniaxiallike pressure.

In this study, the effects of annealing under tellurium vapor have been investigated for Fe 1.03 Te 0.8 Se 0.2 single crystals. The as-grown crystal is not superconducting. After annealing it at 400 • C for 250 h in tellurium (Te) vapor, it shows metallic resistivity temperature dependence below 150 K and a sharp superconducting transition at 13 K. The sample also shows a full magnetic shielding effect at low temperatures. The improvement in superconductivity has been attributed to the removal of excess Fe, which is inevitably incorporated in the as-grown crystals, by the annealing.