arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1607.04724cond-mat.dis-nncond-mat.softcond-mat.stat-mech
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随机磁场中海森堡自旋玻璃的亚稳极小值

The metastable minima of the Heisenberg spin glass in a random magnetic field

Auditya Sharma, Joonhyun Yeo, M. A. Moore

摘要:

我们研究了在$m$ -分量随机场(强度为$h_{r}$)存在下,经典$m$ -矢量分量自旋玻璃中的零温亚稳态,包括Sherrington Kirkpatrick(SK)模型,Viana Bray(VB)模型和具有长程幂律相互作用的随机稀释一维模型.对于SK模型,我们已经分析计算了它的复杂性(最小值的对数)退火的情况下和淬火的情况下,无论是在德阿尔梅达无源(AT)字段($h_{AT} > 0$为$m>2$)以上和以下的字段。我们已经做了淬火从一个随机的初始状态,把自旋平行于他们的本地领域,直到收敛,并发现在零领域,它总是产生最小值有零重叠彼此。对于SK模型中的$m=2$和$m=3$情况,在猝灭中达到的最终能量非常接近于状态重叠将获得副本对称性破缺特征的能量$E_c$。这些最小值具有边际稳定性,并且它们之间具有长期相关性。在SK极限下,我们分析研究了退火近似下海森矩阵的态密度$ρ(λ)$。尽管不存在连续对称性,但对于$h_{r}<h_{AT}$的态密度,谱以通常的$\sqrtλ$形式向下延伸到零。然而,当$h_{r}>h_{AT}$时,在光谱中存在间隙,该间隙随着接近$h_{AT}$而闭合。对于VB模型和其他模型,我们的数值计算表明,总是存在一些低的特征值,似乎从来没有一个差距。对于除SK模型之外的任何模型,在从无限温度到达的淬火态中没有AT转变的迹象,SK模型是唯一的在$h_{AT}$之上具有零复杂性的模型。

英文摘要:

We have studied zero temperature metastable states in classical $m$-vector component spin glasses in the presence of $m$-component random fields (of strength $h_{r}$) for a variety of models, including the Sherrington Kirkpatrick (SK) model, the Viana Bray (VB) model and the randomly diluted one-dimensional models with long-range power law interactions. For the SK model we have calculated analytically its complexity (the log of the number of minima) for both the annealed case and the quenched case, both for fields above and below the de Almeida Thouless (AT) field ($h_{AT} > 0$ for $m>2$). We have done quenches starting from a random initial state by putting spins parallel to their local fields until convergence and found that in zero field it always produces minima which have zero overlap with each other. For the $m=2$ and $m=3$ cases in the SK model the final energy reached in the quench is very close to the energy $E_c$ at which the overlap of the states would acquire replica symmetry breaking features. These minima have marginal stability and will have long-range correlations between them. In the SK limit we have analytically studied the density of states $ρ(λ)$ of the Hessian matrix in the annealed approximation. Despite the absence of continuous symmetries, the spectrum extends down to zero with the usual $\sqrtλ$ form for the density of states for $h_{r}<h_{AT}$. However, when $h_{r}>h_{AT}$, there is a gap in the spectrum which closes up as $h_{AT}$ is approached. For the VB model and the other models our numerical work shows that there always exist some low-lying eigenvalues and there never seems to be a gap. There is no sign of the AT transition in the quenched states reached from infinite temperature for any model but the SK model, which is the only model which has zero complexity above $h_{AT}$.

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