Superconducting currents from molecular theory

Abstract

The gauge‐invariant method of London is used to solve the molecular orbital (MO) equations in a square planar slab, with one electron per site, in a perpendicular magnetic field. Pair currents appear because of the degeneracy and incomplete filling of highest occupied molecular orbital (HOMO). This type of electronic structure may alternatively result in an antiferromagnetic (AF) state or a charge density wave (CDW) state. The CDW state has alternating oxidation states which are different in two units, for example, in BaBiO3, where the valence state of Bi is alternating between +3 and +5, depending on whether the Bi6s2 electron pair is present at the site. The AF state, on the other hand, appears if only the middle valence state is stable. It is shown here that appearance of electron pair currents requires that all three oxidation states are at about the same total energy. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 543–548, 1999

On the superconductor mechanism of [bis(ethylenedithio)tetraselenafuvalene]2GaCl4

“…Density functional theory calculations showed that the organic superconductor [BETS] 2 GaCl 4 has a non-uniform electronic structure at the Fermi surface with half-filled orbitals, as generally found for type II superconductors [29][30][31][32]. The half-filled orbitals couple to local open-shell singlet states creating available sites for two excess electrons to form the Cooper pair.…”

Correlations between Spectra and Resistivity in Transition Metal Oxides

“…SC currents are possible, if the intervening electron system [Cu­(II)­Cu­(II)] interacts with the precurser state and the successor state. , Since we know that there is a phase transfer from antiferromagnetic to charge alternant we know that Cu­(I)­Cu­(III) at one moment has the same energy as Cu­(II)­Cu­(II) (Figure ). The possibility for electron pair transfer with D = 0 is an experimental fact. , Doping is capable of changing the relative order in free energies of spin ordered and charged state in local mixed-valence systems.…”

“…The aim of the present paper is to consider pairing from a localized (or correlated) point of view, ,, when it converges to an intinerant behavior. Cuprates but not vanadates may become SC, even if U is about the same (2 eV).…”

Effect of Pressure on Superconducting Properties

“…2 States and orbital occupancy in the three possible states. Wave functions in parenthesis orbitals, interact with (ab + ba) to form the superconducting ground state [33,34]. Polarization by the alkali ions (not shown) makes the system stable, but does not affect the relative energy levels very much.…”