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arXiv 0905.0482cond-mat.dis-nncond-mat.stat-mech
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相互作用Ising自旋的集体动力学:Bethe晶格的精确结果

Collective dynamics of interacting Ising spins: Exact results for the Bethe lattice

A. L. Burin, N. V. Prokofev, I. S. Tupitsyn

摘要:

本文研究了分子磁体薄膜的低温动力学行为,即:e.由在其基态具有大电子自旋S的分子组成的晶体。电子自旋动力学通过耦合到核自旋浴来介导;这种耦合允许在共振条件下,当其他电子自旋的磁偶极场中的塞曼能量的变化通过与核自旋的相互作用来补偿时,在它们的两个能量最小值Sz=+- S之间的一小部分电子自旋的跃迁。共振自旋的跃迁可以导致在它们的邻居中打开或关闭共振,从而导致在共振自旋的足够大的密度P0下的集体动力学。我们建立并求解了自旋与z个近邻相互作用的Bethe晶格(BL)的等效动力学渗流问题,发现系统在P_{0} = Pc 1 ~ exp(-1/3)/(3 z)和P0= Pc 2 ~ exp(-1)/z处存在一个(2<z<6)或两个(z > 5)动力学跃迁,这取决于共振自旋密度P0和近邻数目z.前一个跃迁是连续的,并与一个无限大的耦合共振自旋团簇的形成相关联,类似于发生在P0 ~ 1/z处的静态渗流跃迁。后一个跃迁,z>5,是不连续的,并且与共振自旋密度从小值~ 1/z到接近1的瞬时增加相关联。我们的研究结果的实验意义进行了讨论。

英文摘要:

We study the low temperature dynamics in films made of molecular magnets, i. e. crystals composed of molecules having large electronic spin S in their ground state. The electronic spin dynamics is mediated by coupling to a nuclear spin bath; this coupling allows transitions for a small fraction of electronic spins between their two energy minima, Sz=+- S, under resonant conditions when the change of the Zeeman energy in magnetic dipolar field of other electronic spins is compensated by interaction with nuclear spins. Transitions of resonant spins can result in opening or closing resonances in their neighbors leading to the collective dynamics at sufficiently large density P0 of resonant spins. We formulate and solve the equivalent dynamic percolation problem for the Bethe lattice (BL) of spins interacting with z neighbors and find that depending on the density of resonant spins P0 and the number of neighbors z the system has either one (2<z<6) or two (z > 5) kinetic transitions at P_{0}=Pc1 ~ exp(-1/3)/(3z) and P0=Pc2 ~ exp(-1)/z. The former transition is continuous and associated with the formation of an infinite cluster of coupled resonant spins similarly to the static percolation transition occurring at P0 ~ 1/z. The latter transition, z>5, is discontinuous and associated with the instantaneous increase in the density of resonant spins from the small value ~ 1/z to near unity. Experimental implications of our results are discussed.

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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