arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 0804.1342cond-mat.stat-mech
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连续分布随机磁场下的Ising自旋玻璃:三临界点和不稳定线

Ising spin glass under continuous-distribution random magnetic fields: Tricritical points and instability lines

N. Crokidakis, F. D. Nobre

摘要:

在无限程相互作用极限下的伊辛自旋玻璃模型中考虑了随机磁场的影响。随机磁场的概率分布是双高斯分布,其由分别以$+H_{0}$和$-H_{0}$为中心的两个高斯分布组成,呈现相同的宽度$σ$。有人认为,这样的分布是更合适的理论描述的真实系统比其更简单的特定的两个众所周知的限制,即单高斯分布($σ\gg H_{0}$),和双峰的($σ= 0$)。该模型的副本的方法进行了研究,并在副本对称的解决方案,获得相图。对于不同的$σ$值,临界边界会出现三临界点,可能有两个三临界点沿着同一临界边界。据我们所知,这是第一次在连续分布随机场场的存在下验证了自旋玻璃模型的这种行为,这代表了真实系统的典型情况。分析了复制对称解的稳定性,并验证了低温下通常的Almeida-lesser不稳定性。证明了较高温度的三临界点总是出现在复对称解的稳定区域内,并解析地得到了仅出现该三临界点的包含参数$H_{0}$和$σ$的条件.我们的一些结果进行了讨论,在文献中的实验测量。

英文摘要:

The effects of random magnetic fields are considered in an Ising spin-glass model defined in the limit of infinite-range interactions. The probability distribution for the random magnetic fields is a double Gaussian, which consists of two Gaussian distributions centered respectively, at $+H_{0}$ and $-H_{0}$, presenting the same width $σ$. It is argued that such a distribution is more appropriate for a theoretical description of real systems than its simpler particular two well-known limits, namely the single Gaussian distribution ($σ\gg H_{0}$), and the bimodal one ($σ= 0$). The model is investigated by means of the replica method, and phase diagrams are obtained within the replica-symmetric solution. Critical frontiers exhibiting tricritical points occur for different values of $σ$, with the possibility of two tricritical points along the same critical frontier. To our knowledge, it is the first time that such a behavior is verified for a spin-glass model in the presence of a continuous-distribution random field, which represents a typical situation of a real system. The stability of the replica-symmetric solution is analyzed, and the usual Almeida-Thouless instability is verified for low temperatures. It is verified that, the higher-temperature tricritical point always appears in the region of stability of the replica-symmetric solution; a condition involving the parameters $H_{0}$ and $σ$, for the occurrence of this tricritical point only, is obtained analytically. Some of our results are discussed in view of experimental measurements available in the literature.

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。

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