In this article, history, recent development, future perspective of pressure effect on organic superconductors were reviewed. After describing how the organic superconductor was born, pressure-temperature phase diagrams of two representing organic superconductors were introduced. Next we present several examples of various type of the phase diagrams of the organic superconductors that were recently discovered or attracted. Finally, possible strategies for the development of the novel superconductors are mentioned.
Recent advances in pressure-induced superconductivity were reviewed about 3d-metal oxides including high-Tc cuprates, spin-ladders, and Fe-based pnictides. The dome-shaped pressure dependence of critical temperature (Tc) was focused on as a key word throughout this article. The origin of the Tc domes was investigated from viewpoints of crystal structures and magnetic and/or electronic properties.
Since the discovery of a heavy fermion superconductor CeCu2Si2 in 1979, heavy fermion superconductivity has been observed in several rare earth and actinide compounds. Especially the development of high pressure technique and crystal growth makes it possible to investigate the pressure-induced superconductivity in the heavy fermion compounds, possessing magnetic ordering at ambient pressure. In this article, we present recent advances in pressure-induced superconductivity around antiferromagnetic fluctuation, focusing on CeRhIn5 and CeIrSi3.
In this article, recent advances in the fundamental and applied researches on superconductors at high pressure were reviewed. It was described how efficiently modern observation techniques and theories were combined with high pressure to get insight into the properties of solids, liquids, and gases on the molecular level and to explore new superconducting materials.
In this article, we discuss the anomalous transport phenomena in nearly antiferromagnetic metals, like high-Tc cuprates, organic superconductors, and some heavy fermion systems. We also discuss the grand-Kadowaki-Woods relation in heavy fermion systems with general orbital degeneracy. Finally, we investigate the pairing mechanism and the gap structure in iron-pnictide superconductors in terms of the orbital-fluctuation theory based on the multiorbital Hubbard-Holstein model.
In this article, mechanism of superconductivity in strongly correlated electron systems is briefly reviewed paying attention to roles of spin and charge fluctuations. Valence-skip mechanism is also discussed as a potential one for superconductivity with relatively high transition temperature. Recent new developments in the critical-valence-fluctuation mechanism of Ce-based heavy fermions under high pressure are discussed.
We have constructed a 1500-ton deformation DIA (D-DIA) type apparatus (MADONNA) and a 6000-ton Kawai-type multianvil apparatus (BOTCHAN) at SOSEKI laboratory, Geodynamics Research Center (GRC), Ehime University. A newly designed 6-6 type cell has been successfully operated in MADONNA, demonstrating potential importance of this apparatus for rheological studies of materials under the pressure and temperature conditions of the Earth's lower mantle. In contrast, BOTCHAN is designed for synthesizing high-quality sintered bodies of high-pressure phases, as well as to make large single crystals, utilizing its large sample volume. Ultrahard nano-polycrystalline diamond (NPD=HIME-DIA) rods of about 8 mm in both diameter and length have been successfully synthesized using BOTCHAN, which may be used as new anvil material for advancement of high-pressure technology for deep Earth mineralogy.
Aluminum tri-hydride (AlH3) is promising as a hydrogen storage material. Hydrogenation and dehydrogenation mechanism of aluminum still remain unclear and fundamental study of the Al-H system is required to utilize AlH3 as a practical hydrogen storage material. Aluminum is hydrogenated under high pressure and high temperature to clarify the reaction mechanism. The hydrogenation and dehydrogenation process is investigated using an energy-dispersive and an angle-dispersive in situ x-ray diffraction system.
We have recently carried out a neutron powder diffraction experiment at high pressure using nano-polycrystalline diamond as opposed anvils. Although spurious diffraction peaks from these anvils are rather large, a few peaks from Pb sample with 0.7 mm3 volume were clearly observed. Future potential and problem of the current scheme toward neutron diffraction at the highest pressure regime have been demonstrated.