1996 Fiscal Year Final Research Report Summary
Thoretical Study on First-principles Calculation of Lattice Dynamics and Pressure-Induced Superconductivity
| Project/Area Number |
06640476
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | Osaka University |
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Principal Investigator |
SUZUKI Naoshi Osaka Univ., Fac.Engi.Sci., Professor, 基礎工学部, 教授 (40029559)
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| Co-Investigator(Kenkyū-buntansha) |
SHIRAI Masafumi Osaka Univ., Fac.Engi.Sci., Assoc.Professor, 基礎工学部, 助教授 (70221306)
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| Project Period (FY) |
1994 – 1996
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| Keywords | solid iodine / solid bromine / FLAPW method / electronic band structure / frozen-phonon method / electron-lattice interaction / lattice dynamics / superconductivity |
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| Research Abstract |
Electronic band strucutures, electron-lattice interaction, lattice dynamics and superconductivity in high pressure FCC phase of solid iodine and bromine are studied in detail on the basis of the first-principles full-potential LAPW (FLAPW) method and the semi-empirical tight-binding method. The main results are summarized as follows.
1.The obtained band structures have three hole Fermi surfaces, and hence the FCC solid iodine and bromine are typical hole metals. The density of states at the Fermi energy N (E_F) decreases with increasing pressure.
2.Electron-lattice coupling has been evaluated microscopically by the tight binding method in which transfer energies and their derivatives are determined so as to reproduce the first-principles band structures obatined by the FLAPW method. The Fermi surface average of squared electron-lattice coupling <xi^2> increases considerably as the pressure increases.
3.The frequencies of the longitudinal (L) and the transverse (T) phonon modes at the X (0
… More
,0,2pi/a) point in the Brillouin zone (BZ) have been calculated by the frozen-phonon method. The obtained frequencies show hardening with increasing pressure.
4.The phonon spectrum of the whole BZ have been calculated by taking accout of the electron-lattice interaction and by considering only the nearest neighboring short range forces which were determined to reproduce omega_L and omega_T at the X point obtained by the frozen-phonon method. The average of phonon frequency <omega> and that of squared phonon frequency <omega^2> increases significantly as the pressure increases.
5.The value of N (E_F) <xi^2> increases considerably with increasing pressure, but <omega^2> increases more rapidly than N (E_F) <xi^2> as pressure increases. Therefore the dimensionless electron-phonon coupling lambda = N (E_F) <xi^2> /M <omega^2> becomes a decreasing function of pressure. As the results the superconducting transition temperature T_c also decreases with increasing pressure.
The magnitude of T_c is in order of 1 K,which agrees with the experimental results. But, the calculated pressure-dependence of T_c is diffrent from that of observations in iodine. This discrepancy may suggest a necessity of treating the electron-lattice interaction in more first-principles manner. Less
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