Magnetic-Field and Pressure Effects on the Magnetic Excitations in the Disordered Spin-Peierls Systems

1. (1)在Zn-、Si-和ni掺杂的CuGeO_3中，我们研究了晶格二聚化作用下从布里温区边界折叠到Γ点的折叠声子的拉曼散射，发现掺杂抑制了自旋- peierls （SP）跃迁，降低了晶格畸变。我们甚至在轻掺杂样品的反铁磁相中也观察到这种现象，表明在该相中存在晶格二聚化现象。在高掺杂的样品中，其光谱变宽，有一个高能的尾巴，表明存在具有短程晶格二聚化的均匀反铁磁相。(2)在掺杂的CuGeO_3中，选择规则被打破，我们可以观察到SP间隙激发。随着掺杂剂浓度的增加，其能量减小并展宽。随着掺杂浓度的增加，双磁激发结合态转变为谐振态，并最终消失。考虑到磁激励寿命的缩短，利用格林函数对这些特征进行了更理论化的论证。(3)研究了在强磁场作用下不匹配相的磁激励。在不相称相位，SP隙激励转变为类孤子激励，其频率随磁场的增加而增加。另一方面，双磁激发束缚/共振态的强度迅速降低。(4)安装了带有金刚石砧细胞的高压设备，利用拉曼光谱研究高压对SP跃迁的影响。我们发现在室温严格静水压力下，连续的结构相变为辉石岩型结构。辉石型结构已被报道仅在准静水压力下以纯晶体形式出现。(5)众所周知，在重掺杂CuGeO_3中SP相消失。我们通过观察折叠的声子，证明了在低温下对重mg掺杂晶体施加压力时SP相发生了修正。α′- nav_2o_5的拉曼散射(1)在低温相磁激发下观察到三个折叠声子和一阶和二阶拉曼光谱。我们从极化特性的结果推断出低温相的晶格对称性。α′-Na_<1-δ>V_2O_5中Na^+离子的缺乏切断了自旋链，抑制了相变，降低了晶格畸变。我们将这些结果与CuGeO_3进行了比较。(2)我们观察到V^<4+>离子的V- o弯曲声子与d - d电子拉曼带之间的范诺效应。这种效应随着Na +离子缺乏浓度的增加而减弱。考虑到声子-声子弛豫过程，这些光谱在理论上得到了证明。少

1. Raman scattering in CuGeO_3(1) In Zn-, Si- and Ni-doped CuGeO_3, we studied Raman scattering from the folded phonon, which was folded onto Γ point from the Brillouin zone boundary by the lattice dimerization, and found that the doping suppressed the spin-Peierls (SP) transition and reduced the lattice distortion. We also observed it even in the antiferromagnetic phase of the lightly doped samples, indicating the existence of the lattice dimerization in this phase. In the heavily doped samples its spectrum broadened with a higher-energy tail, indicating the existence of the uniform antiferromagnetic phase possessing a short-range lattice dimerization.(2) Breakdown of the selection rule in the doped CuGeO_3 enabled us to observe a SP gap excitation. It decreased in energy and broadened with increasing dopant concentration. The two-magneticexcitation bound state changed into a resonant state and finally disappeared with increasing dopant concentration. These features were demonstrated … More theoretically by using Green's function, taking into account the shortening of the lifetime of the magnetic excitations.(3) We studied the magnetic excitations in the incommensurate phase under high magnetic fields. In the incommensurate phase the SP gap excitation changed to a soliton-like excitation whose frequency increased with increasing magnetic field. On the other hand, the intensity of the two-magnetic-excitation bound/resonant state rapidly decreased.(4) High-pressure equipment with a diamond anvil cell has been installed in order to study the high-pressure effect on the SP transition by means of Raman spectroscopy. We found successive structural phase transitions to the pyroxene-type structures under strictly hydrostatic pressures at room temperature. The pyroxene-type structures have already been reported to emerge in pure crystal only under quasihydrostatic pressures.(5) It is well known that the SP phase disappears in heavily doped CuGeO_3. We demonstrated by observing the folded phonon that the SP phase revised in heavily Mg-doped crystal when the pressure was applied to it at low temperatures.2. Raman scattering in α'-NaV_2O_5(1) We observed three folded phonons and the first- and second-order Raman spectra from magnetic excitations in the low-temperature phase. We inferred the lattice symmetry of the low-temperature phase from the results of the polarization characteristics. The Na^+-ion deficiency in α'-Na_<1-δ>V_2O_5 cut the spin chain, and it suppressed the phase transition and reduced the lattice distortion. We compared these results with CuGeO_3.(2) We observed the Fano effect between the V-O bending phonon and the d - d electronic Raman band of the V^<4+> ion. This effect weakened with increasing concentration of the Na^+-ion deficiency. These spectra were demonstrated theoretically, taking into account a phonon-phonon relaxation process. Less