Solid Hydrogen under Ultra High Pressure

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Solid hydrogen is electrically insulator at low pressure but it is expected to show conductivity under pressure at Mbar region. Our purpose is to detect, the metallization not, by indirect optical measurement, but by more direct, electrical resistance measurement. First of all, we tried to produce ultra-high pressure and to develop the techniques of electrical and magnetic measurement under the produced pressure. In fact, we developed DAC (diamond anvil cell) specially designed for ultra-high pressure and succeeded to make fine electrodes with 5 μm width on the pressure surface of 30 μm diameter and so, we are ready for electrical resistance measurement of solid hydrogen with volume of 〜 10ィイD1-8ィエD1cc. High pressure of 2.25 Mbar was also successfully produced and that the resistance measurement was performed there. This is now the best, record for high pressure experiment. Secondly, on the technical basis established above, we have succeeded in the study of search for metallization an … More d superconductivity under pressure, starting from alkaline earth metal Ca, Vib group of elements such as sulfur (S) and oxygen. Further, we observed, for the first time, the pressure induced superconductivity of ionic crystal CsI and simple organic crystal of CィイD26ィエD2IィイD24ィエD2OィイD22ィエD2. During the experimental process stated above, however, the expected metallization pressure value has changed from previous 1.5 Mbar to 2.5 Mbar. Now, it is reported that, the solid hydrogen is still transparent even under 3.4 Mbar and remains as insulator electrically. Our theoretical group (Miyagi et al.) also estimates that, molecular dissociation of solid hydrogen takes place at pressures at around 4 Mbar where hydrogen is metallic. So, we have to change our experimental program and to produce higher pressure. But, at present, we expect we can reach metallic hydrogen at, pressures between 2 Mbar and 3 Mbar and at temperature of 1000 ℃ 〜 1500 ℃. Now, we started confinement and pressurization of hydrogen. Present results show the difficulty of stable confinement, because of the diffusion into the surrounding metal. There are several difficulties against the metallization of solid hydrogen but still the new experimental techniques are developed and our reports give belief on the successful finding of metallic hydrogen in near future. Less