Thoretical Study on Firstprinciples Calculation of Lattice Dynamics and PressureInduced Superconductivity
Project/Area Number  06640476 
Research Category 
GrantinAid for Scientific Research (C)

Allocation Type  Singleyear Grants 
Section  一般 
Research Field 
固体物性II(磁性・金属・低温)

Research Institution  Osaka University 
Principal Investigator 
SUZUKI Naoshi Osaka Univ., Fac.Engi.Sci., Professor, 基礎工学部, 教授 (40029559)

CoInvestigator(Kenkyūbuntansha) 
SHIRAI Masafumi Osaka Univ., Fac.Engi.Sci., Assoc.Professor, 基礎工学部, 助教授 (70221306)

Project Period (FY) 
1994 – 1996

Project Status 
Completed(Fiscal Year 1996)

Budget Amount *help 
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1996 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1995 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1994 : ¥700,000 (Direct Cost : ¥700,000)

Keywords  solid iodine / solid bromine / FLAPW method / electronic band structure / frozenphonon method / electronlattice interaction / lattice dynamics / superconductivity / 圧力誘起非金属金属転移 
Research Abstract 
Electronic band strucutures, electronlattice interaction, lattice dynamics and superconductivity in high pressure FCC phase of solid iodine and bromine are studied in detail on the basis of the firstprinciples fullpotential LAPW (FLAPW) method and the semiempirical tightbinding 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.Electronlattice coupling has been evaluated microscopically by the tight binding method in which transfer energies and their derivatives are determined so as to reproduce the firstprinciples band structures obatined by the FLAPW method. The Fermi surface average of squared electronlattice 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 frozenphonon 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 electronlattice 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 frozenphonon 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 electronphonon 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 pressuredependence of T_c is diffrent from that of observations in iodine. This discrepancy may suggest a necessity of treating the electronlattice interaction in more firstprinciples manner. Less

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Research Products
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