Bi系超伝導体劈開表面の変調構造

概要

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We have obtained scanning tunneling microscopic (STM) images with atomic resolution on the cleaved surface of Bi_2Sr_2CaCu_2O_<8+δ> and Bi_2Sr_2CuO_<6+δ> single crystals. The images show surface modulated structures characteristic of the Bi-based oxide systems. As well as bulk, the modulation periodicity of the Bi_2Sr_2CuO_<6+δ> surface lattice is incommensurate compared with a primitive unit cell, so that the out-of-plane structure looks like a sinusoidal wave. In the case of Bi_2Sr_2CaCu_2O_<8+δ>, however, the STM image consists of the alternating lines of higher- and lower-position Bi atoms, where a depressed atom row exists at the top of the modulation wave. Unlike bulk, the modulation period is just five times the primitive unit cell. In this report, we propose a new structure model for the surface BiO plane of Bi_2Sr_2CaCu_2O_<8+δ>. Although the cleaved surface is a similar BiO single plane as in the Bi-based oxide systems, the modulated structures are quite different from each other. The oxygen deficiency in the surface BiO plane is thought to be a principal reason for the surface reconstruction and relaxation under ultrahigh vacuum circumstances.
東海大学の論文