Study of the model of hole superconductivity in multiple band cases and its application to transition metals

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:6326644

Hong, X Q

The authors have studied a simple model consisting of a chain of atoms with two atoms per unit cell. This model develops two bands when the inter-cell and intra-cell hopping amplitudes are different. They have found that superconductivity predominantly occurs when the Fermi level is close to the top of the upper band where the wavefunction has antibonding feature both inside the unit cell and between unit cells. Superconductivity occurs only in a restricted parameter range when the Fermi level is close to the top of the lower band because of the repulsive interaction within the unit cell. They find that pair expectation values that 'mix' carriers of both bands can exist when interband interactions other than V12 of Suhl et al are present. But the magnitude of the 'mixed pairs' order parameters is much smaller than that of the intra-band pairs. The V12 of Suhl et al is the most important interband interaction that gives rise to the main features of a two-band model: a single transition temperature and two different gaps. They have used the model of hole superconductivity to study the variation of T(sub c) among transition metal series--the Matthias rules. They have found that the observed T(sub c)'s are consistent with superconductivity of a metal with multiple bands at the Fermi level being caused by the single band with strongest antibonding character at the Fermi level. When the Fermi level is the lower part of a band, there is no T(sub c). As the band is gradually filled, T(sub c) rises, passes through a maximum, then drops to zero when the band is full. This characteristic feature is independent of any fine structure of the band. The position of the peak and the width of the peak are correlated. Quantitative agreement with the experimental results is obtained by choosing parameters of onsite Coulomb interaction U, modulated hopping term Delta-t, and nearest neighbor repulsion V to fit the magnitude of T(sub c) and the positions of experimental peaks.

• Research Organization: California Univ., San Diego, CA (United States)
• OSTI ID: 6326644
• Resource Relation: Other Information: Ph.D. Thesis
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
HOLES
BAND THEORY
SUPERCONDUCTORS
TRANSITION ELEMENTS
SUPERCONDUCTIVITY
TRANSITION TEMPERATURE
CARRIERS
FERMI LEVEL
METALS
ORDER PARAMETERS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
ENERGY LEVELS
PHYSICAL PROPERTIES
THERMODYNAMIC PROPERTIES
360107* - Metals & Alloys- Superconducting Properties- (1992-)