泛函选择对钇钡铜氧超导体能带与电子性质的影响

Effect of Functional Choice on the Band Structure and Electronic Properties of Yttrium Barium Copper Oxide Superconductors

摘要: 高温超导体因其独特的电子性质和非常规超导行为而备受关注。尤其是高能离子注入、压力、电磁场等外部场引起的高温超导材料相变，已成为研究的热点。然而，相关的内在机理仍未完全被揭示。第一性原理计算被广泛认为是一种有效的方法，用以深入探究其内在机理。本研究利用第一性原理计算，探讨了不同泛函(PBE, PBE + U, HSE06)对YBa₂Cu₃O₇ (YBCO₇)中氧缺失现象对电子转移性质及超导性能的影响。结果表明，氧的缺失显著改变能带结构，不同泛函预测的结果有很大偏差，三种不同泛函预测的YBa₂Cu₃O₆ (YBCO₆)的能隙范围分别为0 eV、0.88 eV和1.69 eV。较大的能隙表明材料呈现绝缘态，而没有能隙则表明材料仍保持金属性。通过与实验结果对比，我们发现HSE06泛函在描述该材料的金属–绝缘性相变方面较为合理，且能隙的存在与否主要受铜的$d_{z^2}$ 轨道影响，从PBE泛函计算中发现YBCO₆没有带隙是因为Cu的d_yz轨道占据。此外，O(4)缺失可导致材料c轴伸长，这一现象与实验中He离子辐照后材料的X射线衍射(XRD)分析结果趋势一致。我们的发现将有助于解释YBCO₇在外部场作用下，尤其是He离子辐照引发的金属绝缘相变现象，将为高温超导材料及其器件应用提供理论基础和新思路。

Abstract: High-temperature superconductors have attracted significant attention due to their unique electronic properties and unconventional superconducting behavior. In particular, phase transitions of high-temperature superconducting materials induced by external fields such as high-energy ion implantation, pressure, and electromagnetic fields have become a research hotspot. However, the underlying mechanisms remain not fully understood. First-principles calculations are widely regarded as an effective method to explore these intrinsic mechanisms in depth. In this study, first-principles calculations are employed to investigate the effects of oxygen vacancy phenomena on the electronic transfer properties and superconducting performance of YBa₂Cu₃O₇ (YBCO₇) under different functionals (PBE, PBE + U, HSE06). The results show that oxygen vacancies significantly alter the band structure, with considerable discrepancies observed in the predictions of different functionals. The calculated band gap for YBa₂Cu₃O₆ (YBCO₆) ranges from 0 to 1.69 eV. A larger band gap suggests an insulating state, while the absence of a band gap indicates that the material remains metallic. By comparing the results with the experimental results, we find that the HSE06 functional provides the most reasonable predictions. The presence or absence of a band gap is primarily influenced by copper orbitals. Oxygen vacancy at O(4) can cause the material’s c-axis to elongate, which is consistent with the trends observed in X-ray diffraction (XRD) analysis of materials after He-ion irradiation in experiments. Our findings contribute to explaining the metal-insulator phase transition of YBCO₇ under external fields, especially He-ion irradiation, and provide a theoretical foundation and new insights for the development of high-temperature superconducting materials and their device applications.