Role of Internal Stresses in Electronic Pairing of Layered Superconductors

Physica C: Superconductivity

Kucab

2003

We analyze the itinerant model for antiferromagnetism, which was developed previously by Plischke, Mattis, Brouers and Mizia. In this model we include both; single-site and two-site electron correlations. Including additionally band degeneration into the model allows for considering intraatomic exchange interactions in the Hamiltonian. The modified Hartree-Fock approximation for the two-site interactions is used. This approximation gives the spin band narrowing, which is the same for both spin directions and affects possibility of antiferromagnetic ordering. We use the Green function technique and CPA decoupling. This allows for the change in shape of the spin bands, described by the correlation factors, which decreases kinetic energy of the system. The effective Hartree field and the gain in kinetic energy due to the on-site and inter-site correlation factors drive the antiferromagnetism.

Section: Numerical Examplesmentioning

confidence: 99%

Magnetic ordering of itinerant systems in modified mean field theory: antiferromagnetism

Physica C: Superconductivity

Kucab

2003

“…The kinetic interactions give rise to both of these mechanisms in creating the ferromagnetic state. They were also used in describing the superconductivity [23,24,25,26,27,28,29]. Hirsch [23,24] and Micnas [26] have shown that the interaction ∆t leads to s-wave singlet superconductivity in a less then half-filled band system.…”

Section: Introductionmentioning

confidence: 99%

Coexistence of ferromagnetism and superconductivity: The role of kinetic interactions, kinetic correlations, and external pressure

Kucab

Physica C: Superconductivity

2009

We use the Hubbard type model to describe the coexistence between superconductivity (SC) and ferromagnetism (F). Our Hamiltonian contains single-site and two-site interactions. All inter-site interactions will have included the inter-site kinetic correlation: c + iσ cjσ , within the Hartree-Fock approximation. To obtain the SC transition temperature TSC and Curie temperature TC we use the Green's functions method. The numerical results show that the singlet SC is eliminated by F, but the triplet SC is either enhanced or depleted by F, depending on the carrier concentration and direction of a superconducting spin pair with respect to magnetization. The kinetic correlation is capable of creating superconductivity. We find that the ferromagnetism created by change of the bandwidth can coexist with singlet superconductivity. In the case of triplet superconductivity the ferromagnetism creates different critical SC temperatures for the A1 and A2 phase (the pair's spin parallel and antiparallel to magnetization, respectively).

Role of Internal Stresses and Kinetic Energy Reduction in Layered Superconductors

2002

phys. stat. sol. (b)

Self Cite

74.20.Fg; 74.62.Fj We have considered an extended Hubbard model for the superconducting ceramics. The driving force for superconductivity in the single band model is the nearest-neighbour interaction augmented by the on-site and inter-site volume charge coupling. The transition to superconductivity is also supplemented by the decrease of kinetic energy obtained in the modified mean-field approximation, which is applied to the inter-site interactions. The BCS equation is solved numerically for the single band model with on-site and inter-site Coulomb interaction, and on-site and inter-site volume charge coupling. It is shown, that a physically reasonable set of electron-deformation coupling constants, together with kinetic energy decrease, will significantly lower the nearest-neighbour interaction required for the d-wave superconductivity.