arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2409.10312cond-mat.dis-nn
收藏

稀疏随机图上矢量自旋玻璃模型中的软模

Soft modes in vector spin glass models on sparse random graphs

Silvio Franz, Cosimo Lupo, Flavio Nicoletti, Giorgio Parisi, Federico Ricci-Tersenghi

AI总结:

本文数值研究了稀疏随机图上XY和Heisenberg矢量自旋玻璃模型在零温相变中Hessian矩阵的谱性质,发现两相中最软本征模均局域化,但在相变点Heisenberg模型出现非平庸的CDLEM激发,标志着自旋玻璃相的临界行为。

摘要:

我们数值研究了定义在随机正则图上的矢量自旋玻璃模型低能极小值的 Hessian 矩阵。我们考虑了零温度下的二分量(XY)和三分量(Heisenberg)自旋玻璃,它们受到随机取向外场的作用。改变外场强度,这些模型在零温下经历从高场顺磁体到低场自旋玻璃的相变。我们研究了 Hessian 矩阵的谱性质如何依赖于磁场。特别地,我们研究了相变过程中低频谱的形状和低能特征向量的局域化性质。我们发现,在两相中,谱密度的边缘行为表现为 $λ^{3/2}$:这种行为排除了发散的自旋玻璃磁化率 $χ_{SG}=\langle 1/λ^2 \rangle$ 的存在。对于低能特征向量,我们发现两个模型的两相中最软的本征模总是局域化的。然而,通过详细研究靠近谱下边缘的不同能量尺度上的低能本征模的几何结构,我们发现两模型在相变处表现出不同行为:在 XY 情形下,低能模通常局域化;不同的是,在 Heisenberg 情形下,具有多模结构(类似“离域”)的低能本征模出现在一个于热力学极限下趋于零的能量尺度上。这些几何上非平庸的激发,我们称之为 Concentrated and Delocalised Low Energy Modes (CDLEM),与平庸的局域化激发共存:我们将它们的存在解释为与自旋玻璃相出现相关的临界行为的标志。

英文摘要:

We study numerically the Hessian of low-lying minima of vector spin glass models defined on random regular graphs. We consider the two-component (XY) and three-component (Heisenberg) spin glasses at zero temperature, subjected to the action of a randomly oriented external field. Varying the intensity of the external field, these models undergo a zero temperature phase transition from a paramagnet at high field to a spin glass at low field. We study how the spectral properties of the Hessian depend on the magnetic field. In particular, we study the shape of the spectrum at low frequency and the localization properties of low energy eigenvectors across the transition. We find that in both phases the edge of the spectral density behaves as $λ^{3/2}$: such a behavior rules out the presence of a diverging spin-glass susceptibility $χ_{SG}=\langle 1/λ^2 \rangle$. As to low energy eigenvectors, we find that the softest eigenmodes are always localized in both phases of the two models. However, by studying in detail the geometry of low energy eigenmodes across different energy scales close to the lower edge of the spectrum, we find a different behavior for the two models at the transition: in the XY case, low energy modes are typically localized; at variance, in the Heisenberg case low-energy eigenmodes with a multi-modal structure (sort of ``delocalization'') appear at an energy scale that vanishes in the infinite size limit. These geometrically non-trivial excitations, which we call Concentrated and Delocalised Low Energy Modes (CDLEM), coexist with trivially localised excitations: we interpret their existence as a sign of critical behavior related to the onset of the spin glass phase.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑