Strongly-correlated Electrons in 2-Dimensional Metallic Compounds

1.铜化合物高T_c材料的核磁共振研究揭示了金属态的反常磁性行为，铜自旋上的反铁磁性自旋涨落与载流子浓度、温度有很强的依赖关系。在低载流子浓度下观察到自旋激发带隙(-150K)。核磁共振和核磁共振结果表明，K_3Cu8S_6(层状结构)在金属状态下发生了自旋-电荷分离，随着温度的降低，发生了金属-CDW绝缘体-金属的连续转变。CuS(Layr型)磁激发被理解为弱电子关联的费米液体中的准粒子方案。利用FZ法生长的CuGeO_3(一维结构)，核磁共振研究表明，CuGeO_3(一维结构)的轨道磁化率和超精细相互作用归因于Cu~(2+)&lt；2+&gt；2.Non-Cu化合物在V和O位的自旋晶格驰豫速率(1/T_1)与YBCO中的Cu(1)位的自旋晶格驰豫速率(1/T_1)具有相似的反常温度关系。首次用氧的非化学计量学方法确定了四个相(钙钛矿型)。电子相关系数随着增量的增加而增加，某些相存在自旋电荷分离。在Knight Shift(K)和1/T_1中观察到了V_2O_3的伪自旋能隙行为。LiV_2O_4(尖晶石型)Li-和V-核磁共振揭示了具有重费米子类型的磁激发，这在3D过渡金属化合物中是首次观察到的。CaV_2O_5(一维梯形)的自旋能隙行为类似于SrCuO_2。NaV_2O_5的磁化率服从一维AF-Heisenberg模型，J/K_B=280K。在34K观察到Spin-Peierls转变，这是目前最高的转变温度。

1.Cu compoundsHigh-T_c materials Anomalous magnetic behavior in metallic states is revealed by NMR study.Antiferromagnetic spin fluctuation localized on Cu spins shows strong dependence on carrier concentration, temperature. A gap (-150K) in the spin excitation was observed at low carrier concentration. NMR and NQR results suggest spin-charge separation in metallic states.K_3Cu_8S_6 (layr-type structure) With decreasing temperature, a successive transition, metal-CDW insulator-metal, occurs. The low temperature metallic phase is anomalous metal accompanied by CDW state.CuS (layr-type) Magnetic excitation is understood in a scheme of quasi-particles in Fermi liquid with weak electron correlation.CuGeO_3 (1D structure) Using single crystals grown by an FZ method, NMR study shows the orbital susceptibility and hyperfine interaction are attributed to a Cu^<2+> single ion in orthorhombic crystal field.2.Non-Cu compoundsSrVO_3 (Perovskite-type) Spin-lattice relaxation rate (1/T_1) at V and O sites shows anomalous temperature dependence similar to that of Cu (1) site in YBCO.CaVO_<3-delta> (Perovskite-type) Four phases were first identified with oxygen nonstoichiometry, delta.Electron correlation increases with delta, and spin-charge separation exists in some phases.V_2O_3 Pseudo-spin gap behavior was observed in Knight shift (K) and 1/T_1 in a pressure-stabilized metallic phase.LiV_2O_4 (Spinel-type) Li-and V-NMR revealed a magnetic excitation with heavy fermion-type, which is the first observation in 3d-transition metal compounds.CaV_2O_5 (1D ladder-type) Spin-gap behavior similar to that of SrCuO_2 was observed. The gap was estimated to be 580K.NaV_2O_5 Magnetic susceptibility obeys 1D AF Heisenberg model with J/K_B=280K.Spin-Peierls transition was observed at 34K,which i the highest transition temperature at present.