Browsing by Author "YANG, TJW"

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CORRELATIONS AMONG C/B, TC, AND MADELUNG POTENTIALS IN THE SYSTEM OF RBA2CU3OX SUPERCONDUCTORS
(1989-11-01)
TSAY, SF
;
WANG, SY
;
HORNG, L
;
YANG, TJW
;
電子物理學系
LATTICE RELAX, CHARGE-TRANSFER, AND MADELUNG POTENTIAL-ENERGY IN YBCO SYSTEMS
(1993-12-01)
HORNG, L
;
YANG, TJW
;
電子物理學系
;
Department of Electrophysics
We have calculated Madelung potential energies by Ewald's method in YBa2Cu3-xMxO7-delta system (M = Ni, Zn, Co, Fe, etc.). The Madelung potential energy, long-range Coulomb interaction, is expected to give a major contribution in these partially ionic copper-oxide superconductors, Concerning site preference of dopant ions, the results from the calculated Madelung energies can not only interpret the site preference of dopant ions substituting for copper sites, which are in accordance with most experimental results, but also illustrate strongly that the holes transfer from sheets to chains on substitution. The apical oxygen is a balancing bridge of charge-transfer, and leads to lattice variation of Cu-0 bond length which is due to long-range Coulomb force. These suggest that this kind of charge-transfer channel is one of important factors to affect T(C) values.
ON THE ROLE OF CU-O CHAINS IN YBA2CU3O7-X SYSTEM FROM THE PLASMON-MEDIATED MECHANISM
(1990-08-01)
YANG, TJW
;
TSAY, SF
;
WANG, SY
;
電子物理學系
;
物理研究所
OPTICAL 2ND-ORDER SUSCEPTIBILITY OF COPPER SURFACE DUE TO IMAGE POTENTIAL SURFACE-STATES
(1989-08-01)
WEI, HD
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PAN, RP
;
YANG, TJW
;
電子物理學系
;
電控工程研究所
PLASMON MODES IN A SYSTEM COMPOSED OF CU-O LAYERS AND CHAINS
(1991-06-01)
TSAY, SF
;
WANG, SY
;
YANG, TJW
;
電子物理學系
;
Department of Electrophysics
Based on a free-electron model of both the quasi-two-dimensional CuO2 layers and the quasi-one-dimensional Cu-O chains in high-T(c) Y-Ba-Cu-O superconductors, we have calculated in this simplified system various Coulombic electron-electron interacting potentials V(q), dielectric functions, dispersion relations, and various plasmon modes, including in particular the acoustic plasmons. The main contribution of the chains is to stabilize, isolate, and generate more acoustic plasmons-omega- which provide a pairing mechanism for high-T(c) superconductivity.
RESONANCE RAMAN-SCATTERING IN PYRITE RUS2
(1989-09-01)
LEE, MC
;
HUANG, CR
;
YANG, TJW
;
HUANG, YS
;
LIN, SS
SURFACE SUPERCONDUCTIVITY OF SHORT COHERENCE LENGTH SUPERCONDUCTORS
(1994-12-01)
YANG, TJW
;
CHEN, JL
;
電子物理學系
;
光電工程學系
;
Department of Electrophysics
Based on the microscopic theory of Valls et al for short coherence length superconductors, the surface critical temperature T-cs is assumed to be higher than the bulk critical temperature T-cb and the term of surface energy is added in the Ginzburg-Landau (GL) free energy. A boundary condition is obtained and used to solve the GL equation exactly under zero magnetic field for various temperatures. Two examples are given. The critical temperature Tc will be enhanced by reducing the thickness of a superconducting thin film. The nucleation field H-c3 (T) is proportional to T-cb - T near T-cb; and H-c3 (T) is also proportional to (T-c - T)(1/2) near Tc.
THE COUPLING NATURE OF PLASMON MODES AMONG DIFFERENT LAYERS IN A-SYSTEM COMPOSED OF CUO2 LAYERS AND CUO CHAINS
(1991-12-01)
YANG, TJW
;
TSAY, SF
;
WANG, SY
;
電子物理學系
;
Department of Electrophysics
Using free electron gas model for sheets and chains, we obtain the dielectric function epsilon(q, omega) of a finite multilayer system composed of CuO2 sheets and CuO chains including the Coulomb interactions among layer-layer, chain-chain and chain-layer within the random-phase approximation (RPA). And then the dielectric function epsilon(q. omega) is diagonalized to find eigenvectors for different plasmon modes. Eigenvectors of the lowest (highest) frequency plasmon model for n = 4 and 5 systems are illustrated. We find that the range of Coulomb interactions strongly affects eigenvectors and plasmon dispersion.
THE DISPERSION-RELATIONS OF PLASMONS IN A SIMPLIFIED SYSTEM OF CUO2 LAYERS AND CU-O CHAINS
(1992-09-01)
TSAY, SF
;
WANG, SY
;
YANG, TJW
;
電子物理學系
;
Department of Electrophysics
A simplified model for YBa2Cu3O7 system composed of CuO2 layers and Cu-O chains has been calculated with the long range effect of the all-neighbors Coulombic e-e interactions taken into consideration. Dispersion relations have been worked out and discussed. The most striking consequence from the all-neighbors interaction is that the plasmons have, in the long wavelength limit, in addition to the usual vanishingly small two-dimensional acoustic plasmon energies which result from only nearest neighbor interactions, a non-zero omega(P)* consistent with the bulk plasma frequency of a three dimensional system. The data of an optical reflectance from an EELS experiment has been refitted based on calculated results for plasmon dispersion relations in the YBa2Cu3O7 system.
THE MECHANISM OF CHAINS IN PRODUCING ACOUSTIC PLASMONS IN SYSTEMS COMPOSED OF CU-O2 LAYERS AND CU-O CHAINS
(1990-12-24)
TSAY, SF
;
WANG, SY
;
YANG, TJW
;
電子物理學系
;
Department of Electrophysics
Based on the Coulombic electron-electron interactions the dielectric functions, dispersion relations and various plasmons are calculated and analyzed for systems containing a finite number of Cu-O layers and chains. Because of the chain's small polarization the chains could serve as a charge reservoir in stabilizing the acoustic plasmons of the layers and for larger q they could provide isolation between neighboring coupled layers yielding more acoustic plasmons.