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| RIKEN Press Release | December 19, 2007 |
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Novel means devised to study riddle of superconductivityInvestigation of 'pseudogap phase' points way to high-temperature superconductors. | |
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Researchers at RIKEN have come a step closer to understanding high-temperature superconductivity through the controlled study of Mott insulators, a mysterious class of materials that are of growing interest in advanced materials research. Superconductivity is a state in which electrons move through a wire or other conductor with zero resistance. Experts believe that one key to elucidating the superconductivity mechanism may reside in a state called the 'pseudogap phase,' which appears just before a substance, such as copper oxide, becomes a superconductor. Postulating that electrons show some order in preparation of the onset of superconductivity, they have tried various approaches to observe pseudogaps. These efforts have failed because direct observation of electron states at high resolution has proved to be impossible, thus the 'hidden order of electrons' remained to be identified. However, the new approach used in this ongoing RIKEN research into advanced materials may help solve the elusive pseudogap riddle. Reporting in the online journal of the American Physical Society, the RIKEN team said they had been able to consistently induce an intervening pseudogap phase of the transition to high temperature superconductivity in a crystal lattice structure. They accomplished this by making stepped advances through the superconductivity transition from the conducting material's normal metallic state. As they did, they focused attention on so-called 'Mott insulators,' which they believed could be helpful in understanding what occurs during the transition. When electrons are about to move from one atom to an adjacent atom, they get too close to the electrons that already exist there and are repelled because of the narrow orbit available for electrons to move around in. In this state, electrons stay in their own territories while repelling each other. Therefore, no electric current is produced even when a voltage is applied. This condition produces a Mott insulator, an effect named after its discoverer Nevill Mott. The researchers found that under hydrostatic pressure, intense magnetic manipulation, and low temperatures that were stepped increasingly downward in controlled fashion, they could induce and investigate the transition to the superconducting state, then back again to the metallic state. Through various trials viewed under an electron scanner they determined that the elusive pseudogap phase could be induced at the periphery of Mott insulators within the crystal lattice and was reproducible to allow close, detailed study. The authors said this was the first example they know of pressure- and magnetic field-induced Mott transitions being caused in this highly controlled, stepped fashion. Superconductivity is a phenomenon in which the electrical resistance of a substance suddenly becomes zero at a particular temperature (the transition temperature). 'High temperature' in the case of superconductivity is more than minus 113 degrees C, which is the highest temperature to date at which a transition from metallic to superconducting state has been achieved. A wide range of high-temperature superconductors would revolutionize all types of technology that rely on electricity and magnetism.
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| RIKEN, one of Japan's leading research institutes, conducts basic and applied experimental research in a wide range of science and technology fields including physics, chemistry, medical science, biology and engineering. Initially established as a private research foundation in Tokyo in 1917, RIKEN became an independent administrative institution in 2003. For more information, visit www.riken.jp | |
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