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arXiv 1504.01372cond-mat.stat-mech
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堆积三角晶格薄膜中Blume-Emery-Griffiths模型的三临界性

Tricriticality of the Blume-Emery-Griffiths Model In Thin Films of Stacked Triangular Lattices

Sahbi El Hog, H. T. Diep

摘要:

本文研究了三角形晶格薄膜中的Blume-Emery-Griffiths模型,该模型用自旋间的双线性交换相互作用$J$、二次交换相互作用$K$和单离子各向异性$D$三个参数来描述。晶格位$i$的自旋$S\_i$取三个值$(-1,0,+1)$,该模型可以描述He-4的混合相($S\_i =+1,-1$)和He-3($S\_i =0$).利用蒙特卡罗模拟,我们证明了在低于(高于)$D$的临界值时,跃迁为二(一)级.一般来说,He-3浓度的温度依赖性随层而不同。在有限的温度下,在超流相,膜表面显示出赤字的He-4相对于内层。然而,表面相互作用参数的影响可以扭转这种情况。薄膜厚度对物理性能的影响也将显示为温度的函数。

英文摘要:

We study in this paper the Blume-Emery-Griffiths model in a thin film of stacked triangular lattices.The model is described by three parameters: bilinear exchange interaction between spins $J$, quadratic exchange interaction $K$ and single-ion anisotropy $D$. The spin $S\_i$ at the lattice site $i$ takes three values $(-1,0,+1)$.This model can describe the mixing phase of He-4 ($S\_i =+1,-1$) and He-3 ($S\_i =0$) at low temperatures.Using Monte Carlo simulations, we show that there exists a critical value of $D$ below (above) which the transition is of second-(first-)order.In general, the temperature dependence of the concentrations of He-3 is different from layer by layer. At a finite temperature in the superfluid phase, the film surface shows a deficit of He-4 with respect to interior layers. However, effects of surface interaction parameters can reverse this situation. Effects of the film thickness on physical properties will be also shown as functions of temperature.

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