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arXiv 2212.14656cond-mat.str-elcond-mat.supr-con
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掺杂二维 Hubbard 模型中的公度与非公度磁序:动力学平均场理论分析

Commensurate and incommensurate magnetic order in the doped two-dimensional Hubbard model: dynamical mean-field theory analysis

I. A. Goremykin, A. A. Katanin

AI总结:

本文提出处理螺旋磁序的动力学平均场理论与 Bethe–Salpeter 磁化率方法,揭示 t-t′ Hubbard 模型中磁序随掺杂由反铁磁到非公度再到顺磁相的演化,并复现 La₂CuO₄ 自旋波色散。

摘要:

我们发展了一种用于螺旋磁序的动力学平均场理论方法,转换到自旋沿 z 轴择优排列的局域坐标系中,从而可由处理自旋对角局域格林函数的杂质求解器加以考虑。此外,我们在局域坐标系中求解了非均匀动力学磁化率的 Bethe–Salpeter 方程。我们将该方法应用于描述 t-t′ Hubbard 模型(t′=0.15)中磁序随掺杂的演化,该模型适合描述掺杂的 La₂CuO₄ 高温超导体。我们发现,随着掺杂增加,反铁磁序先转变为 (Q,π) 非公度序,随后转变为顺磁相。费米能级处的谱权重在半填充附近受到抑制,并随掺杂持续增加。反铁磁相中空穴的色散与 t-J 模型研究结果定性一致。在非公度相中,我们发现两支空穴色散,其中一支穿过费米能级,所得费米面形成空穴口袋。我们还研究了由非局域动力学磁化率得到的磁激发色散。横向自旋激发是无隙的,满足 Goldstone 定理;与平均场方法不同,所得磁态被证明是稳定的。纵向激发具有小能隙,表明自旋激发具有刚性。对于符合实际的跃迁和相互作用参数,我们复现了实验测量的 La₂CuO₄ 自旋波色散。

英文摘要:

We develop a dynamical mean-field theory approach for the spiral magnetic order, changing to a local coordinate frame with preferable spin alignment along the $z$-axis, which can be considered with the impurity solvers treating the spin diagonal local Green's function. We furthermore solve the Bethe-Salpeter equations for nonuniform dynamic magnetic susceptibilities in the local coordinate frame. We apply this approach to describe the evolution of magnetic order with doping in the $t-t'$ Hubbard model with $t'=0.15$, which is appropriate for the description of the doped La$_2$CuO$_4$ high-temperature superconductor. We find that with doping the antiferromagnetic order changes to the $(Q,π)$ incommensurate one, and then to the paramagnetic phase. The spectral weight at the Fermi level is suppressed near half filling and continuously increases with doping. The dispersion of holes in the antiferromagnetic phase shows qualitative agreement with the results of the $t$-$J$ model consideration. In the incommensurate phase we find two branches of hole dispersions, one of which crosses the Fermi level. The resulting Fermi surface forms hole pockets. We also consider the dispersion of the magnetic excitations, obtained from the non-local dynamic magnetic susceptibilities. The transverse spin excitations are gapless, fulfilling the Goldstone theorem; in contrast to the mean-field approach the obtained magnetic state is found to be stable. The longitudinal excitations are characterized by a small gap, showing the rigidity of the spin excitations. For realistic hopping and interaction parameters we reproduce the experimentally measured spin-wave dispersion of La$_2$CuO$_4$.

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