The non-hexagonal flux-line lattice in superconductors

Hampshire, DP

Abstract

A generalized form of Ginzburg-Landau theory is proposed which explains the non-hexagonal flux-line lattice found both in metallic and magnetic superconductors without invoking any anisotropic material-dependent properties. The Gibbs energy density postulated for magnetic superconductors (g) is of the form g(B,T)=alpha\psi\(2)+1/2 beta\psi\(4)+[1/(2m)]\(-ih del -2eA)psi\(2)+integral (B/mu (0)-M-ions).dB-(B/mu (0)-M-ions).(mu M-0+mu H-0(ext)) where M is the total local magnetization, M-ions is the local magnetization of the magnetic ions and H-ext is the externally applied field strength. The macroscopic Gibbs energy density and magnetization close to the upper critical field have been calculated for all possible periodic flux-line lattice structures, for high and low values of the Ginzburg-Landau constant (kappa) in both metallic and magnetic superconductors. The generalized theory is consistent with standard theory for high-kappa metallic superconductors. However, for low-kappa and/or strongly paramagnetic superconductors for which (1+chi ')/2 < kappa (2)<3.45(1+chi ')(2)/(1-chi ')(2), where chi ' is the differential susceptibility of the paramagnetic ions in the normal state, non-hexagonal flux-line lattice structures occur. When the flux-line lattice is non-hexagonal, (partial derivative <M-SC>/partial derivative <H-ext>)(Hext approximate to HC2)=(1-chi ')/(3+chi '). Ferromagnetic and antiferromagnetic superconductivity occur when chi ' >1. Furthermore, increasingly strong paramagnetism coexisting with superconductivity can produce a type I-type II phase transition. Experimental evidence for these phenomena and for a correlation between strong paramagnetism in magnetic superconductors and re-entrant superconductivity is discussed.

Citation

Hampshire, D. (2001). The non-hexagonal flux-line lattice in superconductors. Journal of Physics: Condensed Matter, 13(27), 6095-6113. https://doi.org/10.1088/0953-8984/13/27/304

• Journal Article Type: Article
• Publication Date: 2001-07
• Journal: Journal of Physics: Condensed Matter
• Print ISSN: 0953-8984
• Electronic ISSN: 1361-648X
• Publisher: IOP Publishing
• Volume: 13
• Issue: 27
• Pages: 6095-6113
• DOI: https://doi.org/10.1088/0953-8984/13/27/304
• Keywords: CUBIC SUPERCONDUCTORS; MAGNETIC-PROPERTIES; VORTEX LATTICES; NORMALSTATE; SYMMETRY; TRANSITION; SR2RUO4; PHASE; COEXISTENCE; MOLYBDENUM
• Public URL: https://durham-repository.worktribe.com/output/1589818