Defects as a cause of continuity of normal-incommensurate phase transitions
Defects as a cause of continuity of normal-incommensurate phase transitions
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DOI：
10.1103/physrevb.62.12014
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发表时间：
1999-12
影响因子：
3.7
通讯作者：
A. Cano;A. Levanyuk
中科院分区：
文献类型：
--
作者：
A. Cano;A. Levanyuk
几乎所有实验上观察到的正常-无公度相变都是连续的。我们表明，没有任何理论上的原因，这种一般行为在完美的晶体。离平均场三临界点不太远的正态-非公度相变应该是不连续的，而且迄今为止报道的正态-非公度相变离这一点很远是极不可能的。为了理解这种行为，我们研究了缺陷对纯材料中假设的一阶正态-不相称相变的影响。我们发现，这种影响与其他类型的一级相变有着显著的不同。序参量在跃迁处的不连续性的变化是负的，并且在我们的近似理论中形式上是发散的。同时，相变温度的降低仍然有限。我们解释这些结果表明，至少有一些观察到的看似二阶正常的不相称的过渡将在无缺陷的晶体的一阶过渡。
Almost all normal-incommensurate phase transitions observed experimentally are continuous. We show that there is not any theoretical reason for this general behaviour in perfect crystals. A normal-incommensurate phase transition that is not too far from the mean-field tricritical point should be discontinuous and it is highly improbable that so far reported normal-incommensurate phase transitions lie very far from this point. To understand this behaviour we study influence of defects on a hypothetical first-order normal-incommensurate phase transition in a pure material. We have found that this influence is strikingly different from that on other kinds of first-order phase transitions. The change of the discontinuity of the order parameter at the transition is negative and formally diverges within our approximate theory. At the same time the diminishing of the phase transition temperature remains finite. We interpret these results as an indication that at least some of the observed seemingly second-order normal-incommensurate transitions would be first-order transitions in defectless crystals.