Influence of anharmonicity on superconductivity

Journal Article · Wed Feb 01 04:00:00 EST 1978 · Sov. Phys. - JETP (Engl. Transl.); (United States)

OSTI ID:6556355

Karakozov, A E; Maksimov, E G

The method of functional differentiation is used to obtain equations for the Green function of electrons in a superconductor making full allowance for anharmonic interactions. It is shown that these equations are formally identical with the well-known Eliashberg equations. The main difference is that the equations allowing for the lattice anharmonicty have to be modified by replacing the spectral density of the one-phonon Green function occurring in the Eliashberg equation with the dynamic part of a function representing the correlation between this density and the ion concentration. The results obtained demonstrate that allowance for the anharmonicity alters the superconducting properties of a metal for the following reasons: 1) the existence of the Debye--Waller factors in the ionic potential; 2) a change in the spectral density of the one-phonon Green function because of the occurrence of phonon--phonon interactions; 3) many-phonon process; 4) interference effects between one- and many-phonon processes. An analysis is made of the superconductivity of PdH and of the influence of the anharmonicity on the critical temperature T/sub c/ of this compound. It is shown that in this case the greatest influence of the anharmonicity on T/sub c/ is due to the Debye--Waller factors and due to a change in the spectral density of the one-phonon Green function. These two effects reduce the electron--phonon coupling constant of palladium hydride. The effect is greater in PdH than in PdD because of the greater amplitude of the zero-point vibrations of the H atoms. This gives rise to an anomalous isotopic effect in PdH(D).

• Research Organization: P. N. Lebedev Physics Institute, USSR Academy of Sciences, Moscow
• OSTI ID: 6556355
• Journal Information: Sov. Phys. - JETP (Engl. Transl.); (United States), Journal Name: Sov. Phys. - JETP (Engl. Transl.); (United States) Vol. 47:2; ISSN SPHJA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
656102 -- Solid State Physics-- Superconductivity-- Acoustic
Electronic
Magnetic
Optical
& Thermal Phenomena-- (-1987)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANHARMONIC CRYSTALS
CRYSTALS
DEBYE-WALLER FACTOR
FUNCTIONS
GORKOV-ELIASHBERG THEORY
GREEN FUNCTION
HYDRIDES
HYDROGEN COMPOUNDS
PALLADIUM COMPOUNDS
PALLADIUM HYDRIDES
PHONONS
PHYSICAL PROPERTIES
QUASI PARTICLES
SUPERCONDUCTORS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
TRANSITION TEMPERATURE