Electronic structure of crystalline (Nd(0.5)Y(0.5))Ba2Cu3O(7-delta) probed by O1s X-ray absorption spectroscopy

Abstract

The unoccupied density of states near the Fermi level as a function of temperature has been studies by using a crystal of (Nd(0.5)Y(0.5))Ba2Cu3O(7-delta). The fluorescence-yield-mode has been used for the measurement, since the surfaces of the rare-earth HTS (High Temperature Superconductor) materials are not oxygen stable under vacuum conditions. The crystallographic and temperature dependence of the unoccupied density of state near E(sub F) for both tetragonal and orthorhombic crystals were investigated using polarized X-ray absorption spectroscopy of the O1s core level. The O1s absorption spectra measured for orthorhombic crystals at 300 K and 20 K were shown in figures. The O1s absorption spectra at 300 K were found to be consistent with the analogous results for YBa2Cu3O(7-delta)(Y123) with a high oxygen content. The spectra at 20 K was found to have a significant change in shape showing the peaks, for theta = 0 deg, at 528.3 eV and 529.7 eV. This result was consistent with the redistribution of the hole sites and the enhancement of the spectrum by an increase in the number of holes present in the chains.

温度の関数としてのフェルミ準位近傍の空状態密度を(Nd(0.5)Y(0.5))Ba2Cu3O(7-δ)の結晶を用いて研究した。希土類HTS(高温超伝導体)材料の表面は真空下において酸素安定性がないため測定には蛍光生成モードを用いた。正方晶系および斜方晶系結晶について、E(sub F)近傍の空状態密度の結晶および温度依存性をO1sコア準位の分極X線吸収分光法を用いて検討した。斜方晶系結晶に対し300Kと20Kで測定したO1s吸収スペクトルを図に示した。300KにおけるO1s吸収スペクトルは酸素含有量の高いYBa2Cu3O(7-δ)(Y123)に対する類似の結果と一致することが分かった。20Kにおけるスペクトルは形状が著しく変化し、θ=0度に対し、528.3eVおよび529.7eVでピークを示すことが分かった。この結果は、鎖の中に存在する空孔数の増加による空孔の再配分およびスペクトルの増大と一致する。