Metal-insulator transition of Bi2(Sr(2-x)M(x))CuO(y) studied by photoemission and inverse photoemission

Abstract

Measurements of X-ray (XPS) and Inverse-Photoemission (IPES) spectroscopy have been performed on polycrystalline Bi2Sr(2-x)M(x)CuO(y) (M = La, Nd, and Gd, x is greater than 0.4 and less than 0.9 ) ceramics in which metal-insulator transition is observed although Bi2Sr(2-x)Gd(x)CuO(y) is nonsuperconductor. It is found that density of states at the Fermi level is reduced with increasing trivalent ion contents at Sr sites. XPS spectra show that energy shifts of core levels to higher-binding-energy side. The conduction bands of the La-substituted samples are not shifted with the substitution. Changes in the electronic states is discussed in terms of hole concentration.

超伝導体でないにもかかわらず、金属絶縁体転移が観察される多結晶Bi2(Sr(2-x)M(x))CuO(y)(M=La,Nd,Gd、0.4<x<0.9)について、X線誘起光電子分光(XPS)および逆光電子放出(IPES)分光を実施した。フェルミ準位の状態密度は、Sr位置での３価のイオン含量の増加と共に減少することが分かった。XPSスペクトルはコアレベルのエネルギーは高結合エネルギー側へシフトすることを示す。La置換サンプルの伝導帯は置換によってシフトしなかった。電子状態の変化をホール濃度から議論した。