高溫超導體La2-xSrxCuO4中Hubbard模型的適用性

Abstract

本論文中利用同步輻射中心偏極化光源進行O K-edge和Cu L-edge X光近緣吸收光譜(X-ray absorption near edge structure, XANES)實驗，樣品為脈衝雷射蒸鍍系統(Pulse Laser Deposition System, PLD)所製備的La2-xSrxCuO4(0≤ x≤0.4)薄膜。本實驗探討La2-xSrxCuO4薄膜的銅氧平面費米能階(Fermi level；EF)附近能帶之光譜權重(spectral weight)。在La2-xSrxCuO4系統中，量測參雜濃度0 ≤ x ≤ 0.4區域間的樣品以分析其電洞之分佈，同時考慮軸向載子在Zhang-Rice singlet 模型中的影響。並延續著我們團隊在Hubbard model的研究(Y. J. Chen et al., Phys. Rev. B. 88, 134525 (2013))，進而再檢視Peets 等人 (Phys. Rev. Lett. 103, 087402 (2009)) 中對Hubbard model理論預測的質疑。 在La2-xSrxCuO4系統參雜濃度0 ≤ x ≤ 0.4區域間內，我們考慮了軸向載子與銅氧面上載子分布的影響，利用兩種方式估計出的銅氧面上的載子濃度與光譜權重關係，與二維之Hubbard model理論模型比較，符合著二維Hubbard model理論模型的預測。

In this thesis, We measured the x-ray absorption spectroscopy (XAS) of La2-xSrxCuO4(0≤ x≤0.4) thin films which were fabricated by pulse laser deposition technique. We studied the spectral weight at the Sr doping level 0 ≤ x ≤ 0.4 to examine the applicability of the Hubbard model, and followed our previous study by Y. J. Chen et al., Phys. Rev. B. 88, 134525 (2013), compared the results to the theoretical trend proposed by D. C. Peets et al., Phys. Rev. Lett. 103, 087402 (2009). In doped level 0 ≤ x ≤ 0.4 of La2-xSrxCuO4 system, we considered the distribution of the apical holes and the distribution of planar holes on Cu-O plane, compared with the two dimension theoretical Hubbard model. By two different ways considered the planar holes concentration, the experimental results also showed the applicable for two dimension theoretical Hubbard model.