What makes compounds containing fullerenes (soccer-ball-shaped molecules) superconductive? - Strategies on material design for achieving superconductivity at higher temperatures were developed. (Press Release)
- Release Date
- 20 May, 2010
- BL10XU (High Pressure Research)
Durham University (UK)
University of Liverpool (UK)
Japan Synchrotron Radiation Research Institute
RIKEN
Key research findings
• Discovery that fullerene compounds with the same composition have different superconducting critical temperatures and magnetic properties depending on their crystal structure
• Clarification that the superconducting critical temperature of a fullerene-based superconductor with different crystal structures can be explained by a unified model
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An international research group mainly consisting of scientists at Durham University in the UK, University of Liverpool in the UK, Japan Synchrotron Radiation Research Institute (Tetsuhisa Shirakawa, President), and RIKEN (Ryoji Noyori, President) has found that two different crystalline phases exhibit superconductivity in a cesium (Cs)-doped fullerene,*2 which has the highest reported superconducting critical temperature*1 among molecular substances. This was achieved in joint research by Yasuhiro Takabayashi (a postdoctoral researcher) and Professor Kosmas Prassides of Durham University; Alexey Y. Ganin (postdoctoral researcher) and Professor Matthew J. Rosseinsky of the University of Liverpool; Yasuo Ohishi (a senior scientist) at the Japan Synchrotron Radiation Research Institute; and Masaki Takata (chief scientist) at RIKEN SPring-8 Center. In 1991, it was found that a fullerene-based superconductor has the highest reported superconducting critical temperature of Tc=33 K among molecular substances. In 2008, a new Cs-doped fullerene (Cs3C60), which exhibits superconductivity at Tc=38 K under pressure, was discovered, thus breaking the record for Tc for molecular superconductors for the first time in 17 years. According to previous reports, all conventional fullerene-based superconductors doped with alkali metals, such as potassium and rubidium, have the face-centered cubic (fcc) crystal structure. However, the newly discovered Cs3C60, with Tc=38 K, has a body-centered cubic (bcc) structure called A15 (Fig. 1), unlike the above superconductors. Although the fcc crystalline phase of Cs3C60 was also discovered along with the above bcc Cs3C60 with Tc=38 K, its properties have not yet been clarified. In this international joint research, it was clarified that, similarly to the A15 bcc Cs3C60 previously reported, fcc Cs3C60 is an insulator with poor electric conductivity at ambient pressure and that it becomes superconducting at Tc=35 K under pressure. The result of this research revealed, for the first time, that two different crystalline phases of Cs3C60 exhibit superconductivity under high pressure. The crystal structure of Cs3C60 at the pressure and temperature at which it exhibits superconductivity was confirmed using high-brilliance synchrotron radiation at SPring-8. It was also clarified that the superconducting critical temperature of fullerene-based superconductors depends on their bandwidth.*3 The results of this research were published in the British scientific journal Nature on 19 May 2010. Publication: |
<Figure>
The white soccer-ball-shaped spheres represent fullerene molecules. The red balls represent cesium atoms. The closest distance between fullerene molecules is approximately 1 nm (a nanometer is one-billionth of a meter).
temperature of fullerene-based superconductors examined in this research
◯, fcc Cs3C60; □, A15 Cs3C60; ▽, fullerene doped with alkali metal other than Cs3C60. When W is smaller than Wc, Cs3C60 becomes a Mott insulator. Cs3C60 becomes superconducting when W exceeds Wc upon the application of pressure.
<Glossary>
*1 Superconducting critical temperature
The superconductive state is a state in which a substance exhibits zero electrical resistance at a certain temperature or lower, which allows electricity to flow perpetually. The temperature at which the resistance becomes zero is called the superconducting critical temperature, Tc. In superconductive substances, a strong attractive force acts between the electrons, which allows paired electrons to move throughout the crystal.
*2 Fullerene
A molecule predominantly consisting of carbon atoms in the structure of a closed hollow cage. C60 is a particularly well-known fullerene because of its soccer-ball shape and is applied in various functional materials. A recent well-known application of fullerenes is in organic solar cells. American and British scientists won the Nobel Prize in Chemistry in 1996 for their discovery of C60.
*3 Bandwidth
Various properties of a solid, such as the electrical properties, depend on the behavior of a number of electrons moving through the solid, which have different energies. In a solid, electrons fill electron-receiving regions called bands in ascending order of energy. The range of energy in the band is called the bandwidth.
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For more information, please contact: Dr. Masaki TAKATA (RIKEN) |
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- What makes compounds containing fullerenes (soccer-ball-shaped molecules) superconductive? - Strategies on material design for achieving superconductivity at higher temperatures were developed. (Press Release)