Role of doping and oxygen content in superconductivity of La_2 CuO_(4+δ)

ＲｏｌｅｏｆｄｏｐｉｎｇａｎｄｏｘｙｇｅｎｃｏｎｔｅｎｔｉｎｓｕｐｅｒｃｏｎｄｕｃｔｉｖｉｔｙｏｆＬａ_２ＣｕＯ_（４＋δ）￥ＬｉＭｉｎｇ；ＨｕａｎｇＹｕｍｉｎｇ（ＳｃｈｏｏｌｏｆＣｈｅｍｉｓｔｒｙａｎｄＣｈｅｍｉｃａｌＥｎｇｉｎｅｅｒｉｎｇ，Ｓｏｕｔ...

By employing the tight-binding approach based on the extended Huckel molecular orbitals (EHMO), the electronic energy band structures of the Sr-doped La2-x Srx CuO4 and the oxygen-enriched La2CuO4+δ (δ> 0) superconductors were calculated. The results show that both the doping and the oxygen content have a great influence on their electronic structures. The Sr-doping at the La-site causes the band structures to be displaced and the total densities of states at the Fermi level Ef, N(Ef), to in crease greatly. For the oxygen-enriched phase La2CuO4+δ, in addition to the translation of its band structure, the increase in the oxygen content results in the displacement of one d-p hybridization band arising from the copper atom and the peroxide pairs. This change in the band structure leads to the complicated band structure near Ef and the drastic increase in N(Ef), which has an important effect on the physical prop6rties of the La- Cu- O system. In addition, it is demonstrated by the analysis of the band structure results that the peroxide pairs play an important role in the superconductive oxygen-enriched phase.