Ferroelectricity in the ReBa2Cu3O7−δ superconductors

Vibronic origins of highTc

“…Whether or not there is a structural transition to a lower symmetry phase, as has been suggested (Kurtz et al, 1988;Zhang et al, 1988), it would appear that the sizes of the ellipsoids are not markedly affected, otherwise refinement down to a polar phase [explicitly mentioned by Capponi et al, (1987)] would have produced a better fit, as was not in fact the case. Moreover, the same group subsequently demonstrated that a "split atom" refinement in which the chain oxygens were assumed to be off axis and 50% split between two equivalent double well sites, gave a better fit to their structural data (Francois et al, 1988).…”

The peculiarities of the off-center ions dipole-dipole interaction in systems with carriers—narrow-gap ferroelectrics and superconductors

“…For most metals k,a a 1 (a is the lattice constant) aEd interaction (8) stimulate the dipole glass formation. For some metals (both HTSC and narrow-gap semiconductors) are kFa >> 1.…”

“…means the average over carriers ground state (G) (we take the low temperature limit T / p << 1) which is occupied Fermi sphere (ak+IG,) = 0 for lkl(kF) for the normal state and a BCS ground state (PkolGBCS) = 0 for all k) for superconducting state. Both for normal and superconducting states the result could be expressed as: vdd = c shsiJmn (8) where To derive the expression for V,, in r-space it is necessary to know pseudopotential U(k -k') in (6). Expending U(k -k') over Legendre polynoms as it was done in Reference 9 and taking into account only the first term of this expansion, we get approximately U(k -k') = Ud47r.…”

Regularity subsystem of particular temperature points in ferroelectrics and high temperature superconductors

“…High temperature superconductors belong to the ferroelectric-superconductor class of substances (for example, see References [19][20][21][22][23] and have very interesting properties. Therefore they nowadays receive widespread attention and are being extensively studied.…”