Study On The Ground State Of Perovskite-based Mn Oxides

Perovskite-based Mn oxides have abundant phase diagrams, excellent electron polarization properties, and great application potential in CMR effect. They have been one of the forefront fields in Condensed Matter Physics since 1990s.Our deep understanding in electronic and lattice structure of perovskite-based Mn oxides can help us better understand their complexity in electronic and magnetic phase diagrams as well as transportation properties, wich will benefit their application in agriculture, industry or people's everyday life at present and in the future. They are ideal spin injection sources where spin can be injected from inorganic materials to organic or inorganic semiconductors as well as other materials because of their 100% spin polarization. CMR property makes it possible that they can be made into potential p-n junction with excellent function, and they can also be usde in filed-effect devices.Perovskite-based Mn oxides contain many kindes of complex interactions: hopping between the nearest-neighbour e_g electrons, strong Hunder's coupling between the localized core spin of t_2g electrons and the spin of itinerant e_g electon, the nearest-neighbour antiferromagnetic coupling between t_2g electrons, coulomb interaction between e_g electrons, and coupling between e_g electrons and phonons. Many research groups active in this field have done lots of investigations, and they have proposed many different methods and models for perovskite-based Mn oxides, such as the famous one-orbital model and two-orbital model. Based on models available and our deep understanding in complexity of perovskite-based Mn oxides along the z axis, we proposed a new one dimensional single-orbital model. We give the physical meanings of all parts in the hamiltonian and their expressions under the second quantization in detail, and we also give the solution procedure for eigenequations of the system.Using our simple one dimensional model, we choose appropriate parameters for the La_1-xSr_xMnO₃ system, and our computing results can give the AFI-FI transition in slightly doped system, the two phase coexistence in AFI state, and the effect of quenched disorder on spin distribution of the system. Especially, the two phase coexistence in AFI state agrees well with many experimental results and theoretical predictions.People have made much progress in the investigation to perovskite-based Mn oxides. Quantities of theories and experiments reveal that pure double exchage interaction can not describe the complex phase diagrams of the system, nor can it reveal the nature of the complex interaction between charge, orbital, spin and lattice. There are a lot of questions unsolved in this field, such as what is the naure of FM state in the complex phase diagram for this system; the spin glass state in some perovskite-based Mn oxides is the standard spin glass or a phase-separated glass; the dependency between dc resistivity and temperature in perovskite-based Mn oxides, etc. We believe that, with people's deep understanding in this system, more questions will be solved, but some new questions will appear at the same time. In general, with people's rapid progress in understanding this system, the application of perovskite-based Mn oxides will be more and more widely used, wich will be great promotion to the development of our human society!...