Polarization analysis of X-ray absorption at the O 1s absorption edge in PrBa2Cu3O7

Abstract

The polarization dependence of X-ray absorption at the oxygen 1s absorption edge in untwinned LuBa2Cu3O7 and PrBa2Cu3O7 single crystal specimens was measured. The hole states of oxygen in the CuO2 plane in PrBa2Cu3O7 locate at higher energy position than those of the oxygen in the CuO2 in superconducting LuBa2Cu3O7, although the hole states of chain sites remain at the same energy position in both Pr123 and Lu123 samples. Although they are mainly of p sigma character rather than of p pi and were attributed as an upper Hubbard band, a possibility was pointed out that a trace of p pi character hole states in the CuO2 plane exists in Pr123. The formation of Zhang-Rice singlet is suppressed by p pi holes in the CuO2 plane on account of the strong Coulomb interaction on an oxygen site.

非双晶LuBa2Cu3O7およびPrBa2Cu3O7単結晶試験片の酸素1s吸収端におけるX線吸収の偏極依存性を測定した。鎖サイトの空孔状態はPr123およびLu123の両試料とも同一エネルギー位置のままであるが、PrBa2Cu3O7のCuO2面内の酸素の空孔状態は超伝導性LuBa2Cu3O7のCuO2面内の酸素の空孔状態よりも高いエネルギー位置に配位する。それらの空孔はpπ性のものというよりも主としてpσ性のもので、かつ上部Hubbard帯と見なされるが、CuO2面のpπ性空孔状態の痕跡がPr123中に存在する可能性を指摘した。酸素サイトにおける強い電磁相互作用によってCuO2面内のpπ空孔がZhang-Riceの1重項の形成を抑制する。