标题： 磁振子阻尼和量子双交换铁磁体中的模态软化 显示英文标题

标题： Magnon damping and mode softening in quantum double-exchange ferromagnets

摘要： 我们对完全量子双交换铁磁体的磁激发和电子性质进行了全面分析，即铁磁有序源于自旋、电荷和轨道自由度之间的竞争，但不使用经典局域自旋的典型近似。 具体而言，我们研究了类似Kondo晶格模型中的自旋激发，以及靠近轨道选择性莫特相的两轨道Hubbard哈密顿量。 在这些模型中对磁子色散、阻尼和谱权重的计算分析揭示了意想不到的现象，例如磁子模式软化和磁激发的异常退相干，这些现象在早期的实验工作中有所观察，但在此处没有使用声子自由度进行解释。 我们表明，这些效应与费米能级附近的非相干谱特征密切相关，这些特征是由于局域（原位）三重态的量子性质引起的。 这种非相干谱导致了一个类似Stoner的连续谱，自旋激发在此散射，决定了磁子寿命并强烈影响动态自旋结构因子。 我们的研究通过改变电子密度探索了从相干到非相干磁子谱的转变。 此外，我们证明局域自旋的大小通过抑制费米能级附近的非相干谱贡献来减轻退相干。 我们还讨论了有效的$J_1$-$J_2$自旋哈密顿量，该哈密顿量可以准确描述由磁子模式软化表征的大掺杂区域。 最后，我们表明这种行为也存在于具有部分填充轨道的多轨道模型中，即在没有局域自旋矩的系统中，只要模型处于强耦合 regime。 显示英文摘要

摘要： We present a comprehensive analysis of the magnetic excitations and electronic properties of fully quantum double-exchange ferromagnets, i.e., systems where ferromagnetic ordering emerges from the competition between spin, charge, and orbital degrees of freedom, but without the canonical approximation of using classical localized spins. Specifically, we investigate spin excitations within the Kondo lattice-like model, as well as a two-orbital Hubbard Hamiltonian in proximity to the orbital-selective Mott phase. Computational analysis of the magnon dispersion, damping, and spectral weight within these models reveals unexpected phenomena, such as magnon mode softening and the anomalous decoherence of magnetic excitations as observed in earlier experimental efforts, but explained here without the use of the phononic degrees of freedom. We show that these effects are intrinsically linked to incoherent spectral features near the Fermi level, which arise due to the quantum nature of the local (on-site) triplets. This incoherent spectrum leads to a Stoner-like continuum on which spin excitations scatter, governing magnon lifetime and strongly influencing the dynamical spin structure factor. Our study explores the transition from coherent to incoherent magnon spectra by varying the electron density. Furthermore, we demonstrate that the magnitude of the localized spin mitigates decoherence by suppressing the incoherent spectral contributions near the Fermi level. We also discuss the effective $J_1$-$J_2$ spin Hamiltonian, which can accurately describe the large doping region characterized by the magnon-mode softening. Finally, we show that this behavior is also present in multiorbital models with partially filled orbitals, namely, in systems without localized spin moments, provided that the model is in a strong coupling regime.