The Fermi contact term of the hyperfine interaction is derived with a minimum of quantum mechanical assumptions and the use of two different length scales. The latter approach clarifies the mechanism, which has traditionally been subsumed by the term 'contact'.
Charge-order stripes of different types occur when copper oxides are doped with either heterovalent metal, like La 2−x Sr x CuO 4 , or oxygen doped, like Y Ba 2 Cu 3 O 6+y . The difference shows up in the doping dependence of their incommensurability: q c (x) ∝ √ x − p but q c (y) ≈ 0.3. The square-root dependence in the former compound family results from Coulomb repulsion between doped holes (or electrons), residing pairwise in lattice-site O (or Cu) atoms of the CuO 2 planes.The almost constant q c (y) value in the second family results from the aggregation of ozone-like molecules, formed from O 2− ions of the host with embedded oxygen atoms, O, at interstitial sites in the CuO 2 planes. The magnetic moments, m(O), of the lattice-defect O atoms in the first family arrange antiferromagnetically, which gives rise to accompanying magnetization stripes of incommensurability q m (x) = 1 2 q c (x). The ozone complexes have a vanishing magnetic moment, m = 0, which explains the absence of accompanying magnetization stripes in the second family.Embedding excess oxygen as O atoms in CuO 2 planes is likewise assumed for HgBa 2 CuO 4+δ and oxygen-enriched bismuth cuprates. A combination of characteristics from both families is present in oxygen-enriched La 2 CuO 4+y . The validity of determining the hole density in oxygen-enriched cuprates with the universal-dome method is independently confirmed. Besides causing different types of stripes, the two types of lattice-defect oxygen may also cause different types of superconductivity. This could explain the much higher T c,max in oxygen-enriched than Ae-doped cuprates, as well as the cusped cooling-curves of X-ray intensity diffracted by stripes in the former family.
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