Strongly-correlated Electrons in 2-Dimensional Metallic Compounds

1.通过核磁共振研究揭示了Cu化合物高t_c材料在金属态的异常磁性行为。铜自旋上的反铁磁自旋涨落对载流子浓度、温度有很强的依赖性。在低载流子浓度下，自旋激发有-150K的间隙。NMR和NQR结果表明金属态中存在自旋-电荷分离。K_3Cu_8S_6（层状结构）随着温度的降低，发生了金属- cdw绝缘子-金属的连续转变。低温金属相为伴有CDW态的异常金属。用弱电子相关的费米液体准粒子图式来理解cu（层型）磁激发。利用FZ法生长的单晶，核磁共振研究表明，Cu^<2+>单离子在正交晶场中的轨道磁化率和超精细相互作用归因于Cu^<2+>单离子。非Cu化合物ssrvo_3（钙钛矿型）在V和O位点的自旋-晶格弛豫速率（1/T_1）与YBCO中Cu(1)位点的温度依赖性相似。CaVO_<3- δ >（钙钛矿型）首先用氧非化学计量学、δ鉴定出4个相。电子相关性随着δ的增加而增加，在某些相中存在自旋-电荷分离。在压力稳定的金属相中，观察到V_2O_3在Knight shift (K)和1/T_1下的伪自旋间隙行为。LiV_2O_4（尖晶石型）li - V-NMR在三维过渡金属化合物中首次观察到重费米子型磁激发。CaV_2O_5 （1D梯型）的自旋隙行为与SrCuO_2相似。缺口估计是580K。na_2o_5磁化率服从一维AF Heisenberg模型，J/K_B=280K。在34K时观察到自旋-佩尔斯转变，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.