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Register a new userIntramolecular charge ordering in the multi molecular orbital system (TTM-TTP)I_3
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Starting from the structure of the (TTM-TTP)I_3 molecular-based material, we examine the characteristics of frontier molecular orbitals using ab initio (CASSCF/CASPT2) configurations interaction calculations. It is shown that the singly-occupied and second-highest-occupied molecular orbitals are close to each other, i.e., this compound should be regarded as a two-orbital system. By dividing virtually the [TTM-TTP] molecule into three fragments, an effective model is constructed to rationalize the origin of this picture. In order to investigate the low-temperature symmetry breaking experimentally observed in the crystal, the electronic distribution in a pair of [TTM-TTP] molecules is analyzed from CASPT2 calculations. Our inspection supports and explains the speculated intramolecular charge ordering which is likely to give rise to low-energy magnetic properties.
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Using first principle band structure calculations, we critically examine results of resonant x-ray scattering experiments which is believed to directly probe charge and orbital ordering. Considering the specific case of La0.5Sr1.5MnO4, we show that this technique actually probes most directly and sensitively small structural distortions in the system. Such distortions, often difficult to detect with more conventional techniques, invariably accompany and usually cause the orbital and charge orderings. In this sense, this technique is only an indirect probe of such types of ordering. Our results also provide a microscopic explanation of the novel types of charge and orbital ordering realized in this system and other doped manganites.
We have analyzed the experimental evidence of charge and orbital ordering in La0.5Sr1.5MnO4 using first principles band structure calculations. Our results suggest the presence of two types of Mn sites in the system. One of the Mn sites behaves like an Mn(3+) ion, favoring a Jahn-Teller distortion of the surrounding oxygen atoms, while the distortion around the other is not a simple breathing mode kind. Band structure effects are found to dominate the experimental spectrum for orbital and charge ordering, providing an alternate explanation for the experimentally observed results.
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We present angular dependent magneto-transport and magnetization measurements on alpha-(ET)2MHg(SCN)4 compounds at high magnetic fields and low temperatures. We find that the low temperature ground state undergoes two subsequent field-induced density-wave type phase transitions above a critical angle of the magnetic field with respect to the crystallographic axes. This new phase diagram may be qualitatively described assuming a charge density wave ground state which undergoes field-induced transitions due to the interplay of Pauli and orbital effects.
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