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

1.CuGeO_3中的拉曼散射研究(1)在掺锌、掺硅和掺镍的CuGeO_3中，我们研究了折叠声子的拉曼散射，发现掺杂抑制了自旋-Γ(SP)跃迁，减小了晶格的变形。我们甚至在轻掺杂样品的反铁磁相中也观察到了这一现象，表明在该相中存在晶格二聚现象。在重掺杂样品中，它的光谱变宽，具有较高的能量尾部，表明存在具有短程晶格二聚化的均匀反铁磁相。(2)掺杂CuGeO_3的选择规则的破缺使我们观察到SP带隙激发。它的能量随掺杂浓度的增加而减小，并随掺杂浓度的增加而展宽。随着掺杂浓度的增加，双磁激发束缚态转变为共振态，最终消失。这些功能在…中得到了演示在理论上考虑了磁激发态寿命的缩短。(3)研究了强磁场下无公度相中的磁激发态。在无公度阶段，SP间隙激发转变为类孤子激发，其频率随磁场的增大而增加。另一方面，双磁激发束缚/共振态的强度迅速降低。(4)为了利用拉曼光谱研究高压对SP跃迁的影响，安装了带金刚石顶压室的高压装置。我们发现在室温下，在严格的静水压力下，结构相变为辉石型结构。已有报道称，只有在准静水压下才能在纯晶中出现辉石型结构。(5)众所周知，重掺CuGeO_3晶体中的SP相消失。我们通过观察折叠声子证明，在低温加压时，重掺镁晶体中的SP相发生了修正。α‘-NaV_2O_5中的拉曼散射(1)我们在低温相中观察到了三个折叠声子和磁激发的一阶和二阶拉曼光谱。我们从偏振特性的结果推断了低温相的晶格对称性。α‘-Na_&lt；1-δ&Gt；V_2O_5中的Na~+缺位切断了自旋链，抑制了相变，减少了晶格畸变。并与CuGeO_3进行了比较。(2)观察到V^&lt；4&gt；离子的V-O弯曲声子与d-d电子拉曼能带之间的Fano效应。这一效应随缺钠离子浓度的增加而减弱。在考虑声子-声子弛豫过程的情况下，从理论上证明了这些光谱。较少

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