Many-Electron Effects and Phase Transitions in Materials Made of Carbon
| Project/Area Number |
05640374
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | The University of Tokyo |
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Principal Investigator |
TAKADA Yasutami The University of Tokyo, Institute for Solid State Physics, Associate Professor, 物性研究所, 助教授 (00126103)
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| Project Period (FY) |
1993 – 1994
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| Project Status |
Completed (Fiscal Year 1994)
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| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1994: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1993: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | Graphite / Fullerene / Superconductivity / Vertex Corrections / GISC Method / Strong Magnetic Field / Charge-Density Wave (CDW) / Spin-Density Wave (SDW) / バーテックス補正 / プラズモン |
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| Research Abstract |
Much attention is given to graphite and fullerene from both physical and chemical points of view. In this project, we concentrate upon the following two phenomena in which the many-electron effects play an important role : 1. The electronic phase transition in strong magnetic fields in graphite and 2. Superconductivity in alkali-metal doped fullerenes.
Experimentally, an anomaly has been observed in the electronic resistivity at low temperatures in strong magnetic fields in the c direction of graphite. Conventionally, this is considered to appear due to the formation of a charge-density wave (CDW) along the c-axis, but such an explanation is made without a proper treatment of the two inequivalent edges, H-K-H and H'-K'-H' in the Brillouin zone. We take full account of the difference of those edges and reconstructed the gap equation for CDW as well as a spin-density wave (SDW) from first principles in the Hartree-Fock approximation. We obtain the transition temperature T_c by solving the gap equation and find that SDW has a higher T_c that CDW,indicating that SDW rather than CDW is likely to occur in graphite.
In A_3C_<60>, the conduction electrons have a narrow bandwidth which is comparable to the energy of the intramolecular strongly-coupled phonons. Thus we need a strong-coupling theory of superconductivity withvertexcorrections in order to make a quantitative discussion of the pairing mechanism in the system. As a first step to construct such a theory, we develop the gauge-invariant self-consistent (GISC) method and apply it to the fullerenes. We find that the vertex corrections enhance T_c as a whole in the phonon mechanism. We also derive a fundamental theory based on the Baym-Kadanoff's conserving approximation so as to give a firm theoretical basis for GISC.By employing this new theory to investigate the system with a very narrow bandwidth, we find a divergence in the vertex function, indicating an electron-locking effect by local phonons.
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Report
(3 results)
Research Products
(20 results)
