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大西 弘明
Physica Status Solidi (B), 250(3), p.553 - 556, 2013/03
被引用回数：0 パーセンタイル：0(Physics, Condensed Matter)To clarify a role of orbital degrees of freedom in the response to an external field, we investigate the real-time dynamics under applied electric fields in a one-dimensional orbital degenerate Hubbard model, by exploiting numerical techniques. Let us here consider a chain along the 
axis with 
-orbital degrees of freedom on each site and one electron per site. In the ground state, the itinerant 
orbital is singly occupied and the localized 
orbital is empty, while the spin state exhibits antiferromagnetic correlations. After an oscillating electric field is turned on, holon-doublon pairs are created. As the time evolves, the ferro-orbital state is deformed due to the pair-hopping process that is characteristic of multi-orbital systems. Regarding the spin state, we observe the suppression of the antiferromagnetic correlations. We will also address the other filling case.
久保 勝規
Physica Status Solidi (C), 10(3), p.544 - 548, 2013/03
被引用回数：5 パーセンタイル：89.82(Materials Science, Multidisciplinary)We study the periodic Anderson model under a magnetic field by the Gutzwiller method. In this study, we set the Coulomb interaction between 
electrons infinity, and we consider the variational wave function given by 
where ![$$P=prod_{i}[1-n_{f i uparrow}n_{f i downarrow}]$$](/search/images/ERID0XDQOJXWIX11NF4VWMJNNZPXWZRANEQFY3LQMFZHE11XPVXF441GEBUSAXDEN31W2YLSOJXXO5K3EQ.gif)
excludes the double occupancy of electrons at the same site and 
is the number operator of the electron with spin 
at site 
. 
denotes the one-electron part of the wave function. We evaluate energy of the variational wave function by using Gutzwiller approximation, and determine the variational parameters in the one-electron part which minimize energy. Then, spin-dependent effective mass and magnetization under a magnetic field are obtained.
坂井 徹; 中野 博生*
Physica Status Solidi (B), 250(3), p.579 - 582, 2013/01
被引用回数：9 パーセンタイル：40.37(Physics, Condensed Matter)カゴメ格子及び三角格子反強磁性体の磁化過程について、数値対角化と有限サイズスケーリングによって解析した結果を報告する。特に、飽和磁化の3分の1付近における異常な量子臨界現象に焦点を当てる。われわれの以前の解析により、カゴメ格子反強磁性体では、磁化ランプと呼ぶべき新しい量子臨界現象が起きるのに対し、三角格子では従来の磁化プラトーが生じることがわかった。本研究では、カゴメ格子及び三角格子反強磁性体の両方を含む拡張格子模型を考え、磁化ランプと磁化プラトーの間の量子相転移を調べる。
