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Variational Monte Carlo study of the nematic state in iron-pnictide superconductors with a five-orbital model

Chinese Physics B 2015年第1期24卷 109-113页

作者：郑晓军黄忠兵邹良剑 Key Laboratory of Materials Physics Institute of Solid State Physics Chinese Academy of Sciences Faculty of Physics and Electronic Technology Hubei University Beijing Computational Science Research Center Department of Physics University of Science and Technology of China

We perform a variational Monte Carlo study of the nematic state in iron-pnictide superconductors within a realistic five-orbital model. Our numerical results show that the nematic state, formed by introducing an anisotropic hopping order into the projected wave function, is not stable unless the off-site Coulomb interaction V exceeds a critical value. This demonstrates that V plays a key role in forming the nematic state in iron-pnictide superconductors. In the nematic state,the orbital order and the anisotropic spin correlations are consistent with the experimental observations. We argue that the experimentally observed anisotropic magnetic couplings and structural transition are associated with the nematic state and can be understood in a unified framework.

关键词： iron-pnictide superconductors nematic state off-site Coulomb interaction variational Monte Carlo simulation

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STUDIES ON THE NATURE OF THE MACROMOLECULAR CONDENSED state OF 'NASCENT' ULTRA HIGH MOLAR MASS POLYETHYLENE

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Chinese Journal of Polymer Science 2001年第1期19卷 25-31页

作者： Zhong-yong Fan Qiang Lan Hai-shah Bu Li-heng Wu Lin Sun Ren-yuan Qian Shou-xi Chenc Yong-feng Mend Bing-zheng Jiang Department of Materials Science Fudan University Shanghai 200433 Department of Materials Science Fudan University Shanghai 200433 Department of Materials Science Fudan University Shanghai 200433 China Textile 4cademy PO Box 651 Beijing 100025 China Textile 4cademy PO Box 651 Beijing 100025 Institute of Chemistry Chinese Academy of Sciences Beijing 100080 Institute of Chemistry Chinese Academy of Sciences Beijing 100080 Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun 130022 Department of Materials Science Fudan University Shanghai 200433

Ultra high molar mass polyethylene (UHPE) powder as polymerized in a slurry process has been studied, in its nascent state, after recrystallization on rapid cooling from the melt and after hot compression molding to a film, by DSC, effect of annealing the recrystallized specimen at 120 similar to 130 degreesC, morphology by polarizing optical microscopy and small angle X-ray scattering. Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains, involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers. On melting, a nematic rubbery state of nanometer size domain resulted. The nematic-isotropic transition temperature was judged from literature data to be at least 220 degreesC, possibly higher than 300 degreesC, the exact temperature is however not sue because of chain degradation at such high temperatures. The recrystallization process from the melt is a crystallization from a nematic rubbery state. The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity. The remelting peak temperature could be returned close to that of the nascent state by annealing at 120 similar to 130 degreesC.

关键词： ultra high molar mass polyethylene recrystallization remelting annealing nematic state

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