Frustrated quantum-spin system on a triangle coupled with ege_g lattice vibrations - Correspondence to Longuet-Higgins et al.'s Jahn-Teller model -

We investigate the quantum three spin model $({\bf S_1},{\bf S_2},{\bf S_3})$ of spin$=1/2$ on a triangle, in which spins are coupled with lattice-vibrational modes through the exchange interaction depending on distances between spin sites. The present model corresponds to the dynamic Jahn-Teller system $E_g\otimes e_g$ proposed by Longuet-Higgins {\it et al.}, Proc.R.Soc.A.{\bf 244},1(1958). This correspondence is revealed by using the transformation to Nakamura-Bishop's bases proposed in Phys.Rev.Lett.{\bf 54},861(1985). Furthermore, we elucidate the relationship between the behavior of a chiral order parameter ${\hat \chi}={\bf S_1\cdot(S_2\times S_3)}$ and that of the electronic orbital angular momentum ${\hat \ell_z}$ in $E_g\otimes e_g$ vibronic model: The regular oscillatory behavior of the expectation value $$for vibronic structures with increasing energy can also be found in that of$$. The increase of the additional anharmonicity(chaoticity) is found to yield a rapidly decaying irregular oscillation of $$

Chaos and its quantization in dynamical Jahn-Teller systems

We investigate the $E_g \otimes e_g$ Jahn-Teller system for the purpose to reveal the nature of quantum chaos in crystals. This system simulates the interaction between the nuclear vibrational modes and the electronic motion in non-Kramers doublets for multiplets of transition-metal ions. Inclusion of the anharmonic potential due to the trigonal symmetry in crystals makes the system nonintegrable and chaotic. Besides the quantal analysis of the transition from Poisson to Wigner level statistics with increasing the strength of anharmonicity, we study the effect of chaos on the electronic orbital angular momentum and explore the magnetic $g$-factor as a function of the system's energy. The regular oscillation of this factor changes to a rapidly-decaying irregular oscillation by increasing the anharmonicity (chaoticity).Comment: 8 pages, 6 figure

Frustrated quantum three-spins coupled with vibration modes : Quantum chaos in the context of dynamical Jahn-Teller problem(1)Current topics of quantum chaos in nanosciences, Chaos and Nonlinear Dynamics in Quantum-Mechanical and Macroscopic Systems)

この論文は国立情報学研究所の電子図書館事業により電子化されました。本研究では、固体物性論の枠組みで量子カオスを考察する。具体的に、2つのd電子系に含まれる縮退Eg軌道を持つ電子状態(2準位系)と格子振動モードeg(2重縮退の2つの振動モードQ_1,Q_2)が結合した動的ヤーン・テラー系を考察する。その量子ハミルトニアンは線形の電子格子相互作用と非調和ポテンシャルで構成される。後者はHenon-Heiles系と呼ばれるカオスを示す典型的な系と一致する。古典論でこの系がカオスを示すことを数値計算で確かめ、量子系でそのカオスの影響を採る。そして、1)磁気的g因子によってカオスの情報を得ることを提案し、2)さらに、電子遷移スペクトルからもカオスの情報が得られることを示す。最後に、3)電子状態の役割を量子スピンに置き換えた新しいモデルも導入する。それは、3角格子の格子点に反強磁性を示すスピンを並べ、格子振動と結合する系である。この系のフラストレーションを定量化するカイラリティを採用してカオスの量子系における影響を調べる。本講演では特に3)の内容について述べた

Fluorosulfide La2+xSr1−xF4+xS2 with Triple-fluorite Layer Enabling Interstitial Fluoride-ion Conduction

Fluoride-ion conducting solid materials are applicable as solid electrolytes for sensing devices and next generation rechargeable batteries. Most of the previously reported materials have limited to the single-anion compounds such as fluorite-type, tysonite-type, and perovskite-type structures. These are suffered from further improvements by crystal structure modification which derives a paradigm shift in the material tailoring. Fluoride and sulfide ions prefer respective coordination environments because of the different ionic radii and electronegativity. This feature implies that fluorosulfide mixed-anion compounds have potential to form anion-ordering crystal structures with new fluoride-ion conducting layers. Herein, we have found that the fluorosulfide La2+xSr1−xF4+xS2 exhibits fluoride ion conduction. The presence of multiple anions results in the formation of anion-ordering two-dimensional crystal lattice with triple fluorite layers, which cannot be realized for metal fluorides. Sulfide ions in the crystal structure increases the number of interstitial sites of fluoride ions, forming fluoride ion conduction pathway