连续场论中的竞争磁序与自旋残余序
Competing magnetic and spin vestigial orders from continuum field theory
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中文总结 AI 辅助
本研究通过连续场论分析反铁磁与自旋向列相的竞争，发现三相点处一阶转变，并预测顺磁-向列转变的普适类，为Kitaev材料Na₂Co₂TeO₆的有限温度行为提供理论框架。
中文摘要 AI 辅助
我们研究了具有竞争的反铁磁相和自旋向列相的自旋系统，该系统由偶极初级序参量和四极次级序参量描述。反铁磁相同时破缺时间反演和自旋旋转对称性，而向列相仅破缺自旋旋转对称性，可理解为自旋残余相。我们发展了一个包含独立矢量和张量场的经典连续场论，并使用平均场和重整化群方法分析其相和有限温度转变。我们利用关于上临界维数六的ε展开确定不动点结构，并通过微扰固定维数重整化群方法将所得不动点追踪到更低维数。控制反铁磁、向列和顺磁相相遇的多临界不动点在可达分析的维数中均出现在虚耦合处，表明通过三相点的转变是一阶的。远离三相点时，当张量质量足够大时，直接的顺磁到反铁磁转变可以是连续的，无需中间残余相。我们认为该转变在d=3时由立方普适类控制，在d=2时对三分量序参量由伊辛普适类控制。该理论还支持具有中间自旋向列相的两步转变。顺磁到向列转变在d=2时由四态Potts普适类控制，在d=3时为一阶，而向列到反铁磁转变在两种维数下通常预期为连续的伊辛型。我们的结果为理解候选Kitaev材料Na₂Co₂TeO₆中观察到的有限温度转变提供了场论框架。
英文摘要
We study magnetic systems featuring competing antiferromagnetic and spin-nematic phases, described by dipolar primary and quadrupolar secondary order parameters. While the antiferromagnetic phase breaks time-reversal and spin-rotational symmetries, only spin-rotational symmetry is broken in the nematic phase, which can be understood as a spin-vestigial phase. We develop a classical continuum field theory with independent vector and tensor fields and use mean-field and renormalization group methods to analyze its phases and finite-temperature transitions. We determine the fixed-point structure using an $ε$ expansion about the upper critical dimension of six and track the resulting fixed points to lower dimensions using a perturbative fixed-dimension renormalization group approach. The multicritical fixed point governing the meeting of the antiferromagnetic, nematic, and paramagnetic phases occurs at imaginary coupling throughout the dimensions accessible to our analysis, indicating a first-order transition through the triple point. Away from the triple point, a direct paramagnetic-to-antiferromagnetic transition can be continuous when the tensor mass is sufficiently large, without an intervening vestigial phase. We argue that it is governed by the cubic universality class in $d=3$ and the Ising universality class in $d=2$ for three-component order parameters. The theory also supports a two-step transition with an intermediate spin-nematic phase. The paramagnetic-to-nematic transition is governed by the four-state Potts universality class in $d=2$ and is first order in $d=3$, while the nematic-to-antiferromagnetic transition is generically expected to be continuous and of Ising type in both dimensions. Our results provide a field-theoretical framework for understanding the finite-temperature transitions observed in the candidate Kitaev material Na$_2$Co$_2$TeO$_6$.
发表机构
- TU Dresden（德累斯顿工业大学）
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