459 research outputs found
Helicoidal ordering in iron perovskites
We consider magnetic ordering in materials with negative charge transfer
energy, such as iron perovskite oxides. We show that for a large weight of
oxygen holes in conduction bands, the double exchange mechanism favors a
helicoidal rather than ferromagnetic spin ordering both in metals, e.g. SrFeO_3
and insulators with a small gap, e.g. CaFeO_3. We discuss the magnetic
excitation spectrum and effects of pressure on magnetic ordering in these
materials.Comment: 4 pages, 5 figure
Subgap optical absorption in conjugated polymers
We study the quantum lattice motion in conjugated polymers using the Su-Schrieffer-Heeger (SSH) model. We find a strong reduction of the number of relevant lattice degrees of freedom for short chains (up to N = 70 for polyacetylene), which allows us to calculate fully quantum mechanically the linear optical absorption spectrum
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