Fascinating new phases of matter can emerge from strong electron interactions in solids. In recent years, a new exotic class of many-body phases, described by generalized electromagnetism of symmetric rank-2 electric and magnetic fields and immobile charge excitations dubbed \textit{fractons}, has attracted wide attention. Besides having interesting properties in their own right, the models with generalized electromagnetism are also closely related to gapped fracton quantum orders, new phases of dipole-covering systems, as well as quantum information and quantum gravity. However, experimental realization of the rank-2 U(1) gauge theory is still absent and even known practical experimental routes are scarce. In this work, we propose a scheme of coupled optical phonons and nematic degrees of freedom, as well as several concrete experimental platforms for their realizations. We show that these systems can realize the electrostatics sector of the rank-2 U(1) gauge theory. A great advantage of the proposed scheme is that it requires only the basic ingredients of phonon and nematic physics, and hence may be applicable to a wide range of experimental realizations from liquid crystals to electron orbitals.
Elasto-Raman scattering: arsenic optical phonon as a probe of nematicity in BaFe$_2$As$_2$
本文报道了铁基超导体母体化合物BaFe $_2$ As $_2$在可调单轴应变下的Raman散射研究。我们证明了偏振分辨砷（As）声子强度可以用来监测作为温度和应变的函数的砷序参量。在低温下，我们用它来跟踪连续的和可逆的取向下可变应变下的有序相的有序畴。在较高的温度下，应变下的As声子强度的演变反映了接近于$T_S$的增强的极化率。它的温度依赖性下的强应变以下定性的预期行为的伊辛序参量下的对称性破缺场。我们的弹性拉曼研究说明了选择性的各向异性应变相结合的对称解决的探针，如拉曼散射的兴趣。弹性拉曼散射可以应用于各种各样的量子材料，其中单轴应变调谐电子顺序。
Nematic response revealed by coherent phonon oscillations in BaFe$_2$As$_2$
利用光抽运-探测光谱研究了BaFe $_2$ As $_2$的相干声子振荡。时间分辨光学反射率显示出由于$c$轴砷振动的$A_{1g}$相干声子引起的周期性调制。沿正交$a$ -和$b$ -轴偏振的光学探测光束揭示，相干振荡的初始相位显示出作为温度的函数的系统偏差，尽管这些振荡产生于相同的$c$ -轴砷振动。即使在四元结构中，振荡相也保持各向异性，反映了BaFe $_2$ As $_2$的振荡响应。我们的研究表明，光学反射率相干声子振荡的相位的研究可以提供一个独特的证据，一个强耦合的晶格不稳定性的三阶。
Phononic enhancement and detection of hidden spin-nematicity and dynamics in quantum magnets
International Center for Quantum Materials, School of Physics, Peking University（北京大学物理学院量子材料国际中心）；Collaborative Innovation Center of Quantum Matter（量子物质协同创新中心）
Microscopic origin of the nemato-elastic coupling and dynamics of hybridized collective nematic-phonon excitations
Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；Carl Zeiss SMT GmbH（卡尔蔡司SMT有限公司）；Ariel University（阿里埃勒大学）；University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）
Soft-phonon and charge-density-wave formation in nematic BaNi$_2$As$_2$
我们用扩散和非弹性X射线散射研究了BaNi $_2$ As $_2$中的无公度电荷密度波（I-CDW）的形成。在I-CDW的调制矢量$Q_{I-CDW}$周围观察到强烈的漫散射。它在室温下已经可见，并在长程有序状态下坍缩成超结构反射，其中发生小的正交畸变。在$Q_{I-CDW}$周围观察到低能横光学声子模色散的明显下降。声子在冷却时不断软化，最终驱动向I-CDW状态的转变。软声子分支的横向特征阐明了在当前和早期研究中观察到的I-CDW卫星的复杂模式，并解决了I-CDW的单向性的争议。声子不稳定性和它的倒易空间位置被我们的${ab}$ ${initio}$计算很好地捕获。然而，这些都表明费米表面嵌套，也没有增强的动量依赖的电子-声子耦合可以解释I-CDW的形成，证明了它的非常规性质。并提出了I-CDW的替代来源。
