Search

Developing room-temperature superconductor (superconducting at temperature higher than room temperature) is one of our goals of science and technology. Pressure is a powerful tool for investigation of superconductor to improve the properties and to synthesize the target material. Most of superconducting materials show a negative pressure dependence in the superconducting temperature, T c . But some elements show the positive dependence at high pressure. We have been interested not only in the pressure effect on T c but also in the onset of new superconductivity under pressures. Here we review the experimental investigations of pressure-induced superconductivity in elements with developments of high-pressure technique combined with low-temperature equipments. [ABSTRACT FROM AUTHOR]

Superconductivity exceeding 200 K was reported in the highly compressed hydrogen sulfide. The superconducting “material” was found to be synthesized by pressure above 90 GPa by the dissociation of hydrogen sulfide (H 2 S). We have investigated the superconducting properties after the discovery. Here, we report our recent investigations including confirmation the superconductivity and the crystal structure analysis using the synchrotron x-ray at room temperature and low temperature. [ABSTRACT FROM AUTHOR]

The insulating and superconducting states would seem to have very different characteristics. Can any insulator become a superconductor? One proven method, doping an insulating material with carriers, can create itinerant states inside the gap between the conduction and valence bands. Another method is to squeeze the structure by applying pressure. Pressure can expand the bandwidth and also narrow the energy band gap. So the first step to turn an insulator into a superconductor is to make it metallic. Here we review our experimental research and results on superconductivity induced by applying pressure to insulating molecular systems such as elemental molecules. [ABSTRACT FROM AUTHOR]

We have developed complex extreme condition of very low temperature down to 30 mK and very high pressure exceeding 200 GPa by assembling compact diamond anvil cell (DAC) on a powerful 3He/4He dilution refrigerator. Using the apparatus and techniques, we have searched for pressure-induced superconductivity in various materials under pressures. In this paper, our experimental techniques and the examples of pressure-induced superconductivity in Li and Fe are reviewed. [Copyright &y& Elsevier]

Abstract: Pure boron has two allotropes of -rhombohedral boron (-boron) and -rhombohedral boron (-boron) based on icosahedral clusters unit. Pressure-induced metallization and superconductivity of -boron was already reported at pressures above 160GPa. Here we investigate the electrical properties of -boron at Mbar (100GPa) pressure and low temperature. At room temperature the electrical resistivity of -boron decreased with 5 orders by applying pressures up to 160GPa. The temperature dependence of the electrical resistivity recorded at around 160GPa showed superconducting transition at 6K. [ABSTRACT FROM AUTHOR]

We have studied the superconducting properties of CeTIn5 (T=Rh, Ir) under high pressures by means of electrical resistivity measurements and determined the pressure–temperature phase diagrams for the superconducting transition. For both systems, the superconductivity exists in a wide pressure range, 1.5⩽P⩽6.5 GPa for CeRhIn5 and 0⩽P⩽5.2 GPa for CeIrIn5. [Copyright &y& Elsevier]

‘Aromatic hydrocarbon’ implies an organic molecule that satisfies the (4 n + 2) π-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (K x picene, five benzene rings). Its superconducting transition temperatures ( T c ’s) were 7 and 18 K. Recently, we found a new superconducting K x picene phase with a T c as high as 14 K, so we now know that K x picene possesses multiple superconducting phases. Besides K x picene, we discovered new superconductors such as Rb x picene and Ca x picene. A most serious problem is that the shielding fraction is ⩽15% for K x picene and Rb x picene, and it is often ∼1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metal-doped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of T c that is clearly observed in some phases of aromatic hydrocarbon superconductors, suggesting behavior not explained by the standard BCS picture of superconductivity. In this article, we describe the present status of this research field, and discuss its future prospects. [ABSTRACT FROM AUTHOR]

Abstract: We have carried out electrical resistivity experiments on the non-centrosymmetric compound CeIrGe3 under high pressures up to 24GPa. CeIrGe3 is an antiferromagnet with the Néel temperature and a successive magnetic transition at at ambient pressure. With increasing pressure, and merge around 3GPa, becomes unchanged up to 10GPa, and indicates a step-like decrease up to 20GPa. Further increasing pressure, we have found superconductivity above 20GPa with a transition temperature of 1.6K at 24GPa. The upper critical field for the magnetic field along the tetragonal [001] direction is expected to be much larger than 15T. [ABSTRACT FROM AUTHOR]