Electronic States in Two-dimensional Quasicrystals

1.在Al-Pd-Fe和Al-Co体系中制备了晶格常数为几nm的高阶十方相近似晶体。这些近似晶体沿c轴的电阻率表现出金属行为，而伪准晶平面的电阻率比沿c轴的电阻率高一个数量级，并表现出很小的温度依赖性。这些结果与先前得到的十角形准晶体的结果基本相同，并且与Fujiwara等人的理论结果一致，其中（伪）准晶体平面的高电阻率归因于原子簇列中波函数沿c轴的局域化导致的非常大的有效电子质量。用扫描隧道显微镜（STM）观察了由熔体缓慢凝固产生的Al-Co-Ni十方准晶单晶。对氩离子溅射和退火后的十角形准晶体的十倍对称面进行了观察。在-0.1V的偏置电压和1nA的设定电流下获得了STM图像。STM图像通常显示出波长为几nm的不规则斑驳图案，这种图案与Fujiwara等人理论计算的费米能级附近电子波函数振幅的空间分布非常相似，因此观察到的图案被认为反映了电子的空间局域化。从而在很大程度上澄清了二维准晶体中的特殊电子态。

1.High-order approximant crystals of decagonal phase with lattice constants of a few nm have been produced for Al-Pd-Fe and Al-Co systems. The resistivity along the c-axis of these approximant crystals shows a metallic behavior, while the resistivity in the pseudo-quasicrystalline plane is an order higher than that along the c-axis and exhibits very small temperature dependence. These results are essentially the same as those of decagonal quasicrystals previously obtained, and are consistent with the theoretical results obtained by Fujiwara et al.in whihc the high resistivity in the (pseudo-) quasicrystalline plane is attributed to a very large effective mass of electrons as a result of localization of wavefunctions in atomic cluster columns along the c-axis.2.Scanning tunneling microscopy (STM) observation has been made for single crystals of an Al-Co-Ni decagonal quasicrystals produced by slow solidification from the melt. Observation has been made for tenfold-symmetric plane of the decagonal quasicrystal after Ar-ion sputtering and anealing. STM image has been obtained with a bias voltage of -0.1V and a set-current of 1nA.STM images often showed an irregular mottled pattern with a wavelength of a few nm. The pattern is quite similar to that of spatial distribution of the amplitude of the wavefunction of elctrons near the Fermi-level theoreticaly calculated by Fujiwara et al.and hence the observed pattern is considered to reflect the spatial localization of electrons.Thus, the special electronic states in two-dimensional quasicrystals have been experimentally clarified to a large extent.