Valence transition model of the pseudogap, charge order, and superconductivity in electron-doped and hole-doped copper oxides
Valence transition model of the pseudogap, charge order, and superconductivity in electron-doped and hole-doped copper oxides
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DOI：
10.1103/physrevb.98.205153
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发表时间：
2018-07
影响因子：
3.7
通讯作者：
S. Mazumdar
中科院分区：
文献类型：
--
作者：
S. Mazumdar
我们提出了电子和空穴掺杂铜酸盐的价态跃迁模型，其中在掺杂时、电子掺杂化合物中的最佳掺杂或接近最佳掺杂以及空穴掺杂材料中的赝能隙相变时，离子度 Cu$^{2+} \to$ Cu$^{1+}$ 发生离散跳跃。掺杂铜酸盐具有负电荷转移间隙，就像稀土镍酸盐和 BaBiO$_3$ 一样。由于强相关性和小的$d-p$电子跳跃，系统在未掺杂状态下表现为有效的$\frac{1}{2}$填充的Cu带，在掺杂状态下表现为相关二维几何挫败近$\frac{1}{4}$填充的O带。该理论给出了对正常状态下的实验最简单但最全面的理解。传统T$^\prime$晶体中强大的反铁磁性、缺氧在驱动超导中的强大作用以及最佳掺杂时对应于空穴的载流子符号都是同一量子态的表现。在空穴掺杂赝能隙态中，O$^{1-}$-Cu$^{1+}$-O$^{1-}$双轴相当周期4电荷密度波态与破缺的旋转C$_4$对称性共存。这种破缺对称态的有限域将表现出极克尔效应。模型中的超导性是由于 $\frac{1}{4}$ 填充带配对维格纳晶体的不稳定造成的。修订版 B {\bf 93}, 165110 和 {\bf 93}, 205111]。我们假设类似的价态跃迁 Ir$^{4+} \to$ Ir$^{3+}$ 发生在电子掺杂的 SrIr$_2$O$_4$ 中。我们对铜酸盐和铱酸盐做出了可检验的理论预测。最后，我们注意到存在异常大量的非常规超导体，它们表现出接近奇异电荷有序态的超导性，其能带填充也是$\frac{1}{4}$，正是成对维格纳晶体最稳定的地方。
We present a valence transition model for electron- and hole-doped cuprates, within which there occurs a discrete jump in ionicity Cu$^{2+} \to$ Cu$^{1+}$ upon doping, at or near optimal doping in the electron-doped compounds and at the pseudogap phase transition in the hole-doped materials. Doped cuprates have negative charge-transfer gaps, just as rare earth nickelates and BaBiO$_3$. Because of strong correlations and small $d-p$ electron hoppings the systems behave as effective $\frac{1}{2}$-filled Cu-band in the undoped state, and as correlated two-dimensional geometrically frustrated nearly $\frac{1}{4}$-filled O-band in the doped state. The theory gives the simplest yet most comprehensive understanding of experiments in the normal states. The robust antiferromagnetism in the conventional T$^\prime$ crystals, the strong role of oxygen deficiency in driving superconductivity and charge carrier sign corresponding to holes at optimal doping are all manifestations of the same quantum state. In the hole-doped pseudogapped state, a biaxial commensurate period 4 charge density wave state of O$^{1-}$-Cu$^{1+}$-O$^{1-}$ spin-singlets coexists with broken rotational C$_4$ symmetry. Finite domains of this broken symmetry state will exhibit the polar Kerr effect. Superconductivity within the model results from a destabilization of the $\frac{1}{4}$-filled band paired Wigner crystal [Phys. Rev. B {\bf 93}, 165110 and {\bf 93}, 205111]. We posit that a similar valence transition, Ir$^{4+} \to$ Ir$^{3+}$, occurs in electron-doped SrIr$_2$O$_4$. We make testable theoretical predictions on cuprates and iridates. Finally, we note that there exist an unusually large number of unconventional superconductors that exhibit superconductivity proximate to exotic charge ordered states, whose bandfillings are also $\frac{1}{4}$, exactly where the paired Wigner crystal is most stable.