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arXiv 0707.3535cond-mat.supr-concond-mat.str-el
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铜氧化物超导电性的手征元极化子理论

Chiral Plaquette Polaron Theory of Cuprate Superconductivity

Jamil Tahir-Kheli, William A. Goddard

摘要:

用密度泛函从头计算方法对掺杂的La(2-x)Sr(x)CuO 4进行了计算,发现掺杂在面外轨道上产生了局域空穴.一个模型的超导性的基础上开发的假设,掺杂导致形成的四个网站的Cu plaquette组成的平面外A1轨道顶端O pz,平面Cu dz 2,和平面O psigma的孔。这与t-J模型中空穴掺杂到平面Cu dx 2-y2和O psigma轨道中的假设相反。空穴与d9自旋背景的相互作用导致具有顺时针或逆时针电荷流的手征极化子。当LaSrCuO的极化子斑在x~0.05处透过晶体时,形成了Cu的dx 2-y2和平面O的psigma带.自旋交换库仑排斥与手征极化子导致D波超导。声子超导电性中德拜能量的等价物是手征极化子和它的时间反转伙伴之间的最大能量分离。手性极化子诱导的附加斜散射贡献的霍尔效应,并导致一个温度依赖的霍尔效应,适合的LaSrCuO的测量值。由于极化子的手征性和自旋翻转散射以及极化子能量分裂的均匀分布,积分虚极化率满足Ω/T标度。导出的函数形式与实验结果一致。计算了静态自旋结构因子,它与(pi,pi)的分离距离不相称,由~(2 pi)x给出。x2-y2带与极化子的库仑散射导致线性电阻率。x2-y2带与未掺杂Cu d9自旋的耦合导致ARPES赝能隙及其掺杂和温度依赖性。

英文摘要:

Ab-initio density functional calculations on explicitly doped La(2-x)Sr(x)CuO4 find doping creates localized holes in out-of-plane orbitals. A model for superconductivity is developed based on the assumption that doping leads to the formation of holes on a four-site Cu plaquette composed of the out-of-plane A1 orbitals apical O pz, planar Cu dz2, and planar O psigma. This is in contrast to the assumption of hole doping into planar Cu dx2-y2 and O psigma orbitals as in the t-J model. Interaction of holes with the d9 spin background leads to chiral polarons with either a clockwise or anti-clockwise charge current. When the polaron plaquettes percolate through the crystal at x~0.05 for LaSrCuO, a Cu dx2-y2 and planar O psigma band is formed. Spin exchange Coulomb repulsion with chiral polarons leads to D-wave superconductivity. The equivalent of the Debye energy in phonon superconductivity is the maximum energy separation between a chiral polaron and its time-reversed partner. An additive skew-scattering contribution to the Hall effect is induced by chiral polarons and leads to a temperature dependent Hall effect that fits the measured values for LaSrCuO. The integrated imaginary susceptibility satisfies omega/T scaling due to chirality and spin-flip scattering of polarons along with a uniform distribution of polaron energy splittings. The derived functional form is compatible with experiments. The static spin structure factor is computed and is incommensurate with a separation distance from (pi,pi) given by ~(2pi)x. Coulomb scattering of the x2-y2 band with polarons leads to linear resistivity. Coupling of the x2-y2 band to the undoped Cu d9 spins leads to the ARPES pseudogap and its doping and temperature dependence.

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