Probing three-state Potts nematic fluctuations by ultrasound attenuation
Probing three-state Potts nematic fluctuations by ultrasound attenuation
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DOI：
10.1103/physrevb.105.035130
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发表时间：
2021-10
影响因子：
3.7
通讯作者：
K. Kimura;M. Sigrist;N. Kawakami
中科院分区：
文献类型：
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作者：
K. Kimura;M. Sigrist;N. Kawakami
基于最近对魔角扭曲双层石墨烯和掺杂bi2se3的三态波茨向列态的研究，我们分析了临界向列波动对声子低能性质的影响。在这项研究中，我们提出了如何识别波茨三态向列波动超声衰减。高斯涨落分析表明，由于c3断裂键序的涨落，朗道阻尼项具有各向同性，而线虫弹性耦合也具有各向同性。这两个特征导致了横向声衰减系数的各向同性发散和各向同性晶格软化，而c4断裂键序则表现出较强的各向异性。此外，我们使用了平均场近似，并讨论了杂质效应。相变温度在van-Hove奇点填充附近达到最大值，大的态密度有利于向列相转变。结果表明，在较宽的填充范围内，相变为弱一阶相变，随着杂质散射的增加，低温下的一阶相变线逐渐向二阶线偏移，使得相变在较宽的参数范围内为弱一阶相变。进一步证实了在弱一阶相变的情况下，超声衰减系数的增强将在实验中得到明显的观察。
Motivated by recent studies of three-state Potts nematic states in magic-angle twisted bilayer graphene and doped-Bi2Se3, we analyze the impact of critical nematic fluctuations on the low energy properties of phonons. In this study we propose how to identify the three-state Potts nematic fluctuations by ultrasound attenuation. The Gaussian fluctuation analysis shows that the Landau damping term becomes isotropic due to fluctuations of the C3-breaking bond-order, and the nematoelastic coupling is also shown to be isotropic. These two features lead to an isotropic divergence of the transverse sound attenuation coefficient and an isotropic lattice softening, in contrast to the case of the C4-breaking bond-order which shows the strong anisotropy. Moreover, we use a mean-field approximation and discuss the impurity effects. The transition temperature takes its maximum near the filling of the van-Hove singularity, and the large density of states favors the nematic phase transition. It turns out that the phase transition is of weak first-order in the wide range of filling and, with increasing the impurity scattering, the first order transition line at low temperatures gradually shifts towards the second-order line, rendering the transition a weak first-order in a wider range of parameters. Furthermore, it is confirmed that the enhancement of the ultrasound attenuation coefficient will be clearly observed in experiments in the case of a weak first-order phase transition.