用共振软X射线散射研究Bi $_{2.1}$ Sr $_{1.9}$ CaCu $_2$ O $_{8+x}$中布拉格禁戒位置附近的$Q \sim 0$有序
Search for $Q \sim 0$ order near a forbidden Bragg position in Bi$_{2.1}$Sr$_{1.9}$CaCu$_2$O$_{8+x}$ with resonant soft x-ray scattering
摘要：
确定铜氧化物中存在什么样的对称性破缺已经成为一个主要的研究领域。许多作者已经报道了所谓的“$Q \sim 0$“序的证据，这种序涉及空间中均匀的破缺反转、镜像、手征或时间反演对称。并非所有这些观测都得到了很好的理解，需要新的实验探测器。在这里，我们使用共振软X射线散射（RSXS）搜索$Q \sim 0$顺序在Bi $_{2.1}$ Sr $_{1.9}$ CaCu $_2$ O $_{8+x}$（Bi-2212）通过测量区域的禁止布拉格峰，$(0,0,3)$，这是通常熄灭的对称性，但可能成为允许的共振，如果价带顺序存在。使用圆偏振光，我们发现，这种反射成为允许的铜$L_3$共振温度$T_c < T < T^\ast$，虽然仍然没有在线性偏振和在其他温度。这一观察结果表明，在赝能隙温度附近存在空间均匀的价带序。此外，我们观察到周期性振荡的镜面反射率从样品表面，类似薄膜干涉条纹，虽然没有已知的膜。这些条纹是高度共振的，出现在所有的偏振，并表现出一个周期，这取决于光束撞击样品表面的位置。我们推测，这些条纹产生的一些固有的价带不稳定性和外在的结构表面形貌的材料之间的相互作用。我们的研究支持在中等温度下Bi-2212中存在某种$Q \sim 0$对称性破缺态，并呼吁进一步研究使用微聚焦光束，可以从宏观不均匀性中分离微观效应。
英文摘要：
Identifying what broken symmetries are present in the cuprates has become a major area of research. Many authors have reported evidence for so-called "$Q \sim 0$" order that involves broken inversion, mirror, chiral, or time-reversal symmetry that is uniform in space. Not all these observations are well understood and new experimental probes are needed. Here we use resonant soft x-ray scattering (RSXS) to search for $Q \sim 0$ order in Bi$_{2.1}$Sr$_{1.9}$CaCu$_2$O$_{8+x}$ (Bi-2212) by measuring the region of a forbidden Bragg peak, $(0,0,3)$, which is normally extinguished by symmetry but may become allowed on resonance if valence band order is present. Using circularly polarized light, we found that this reflection becomes allowed on the Cu $L_3$ resonance for temperatures $T_c < T < T^\ast$, though remains absent in linear polarization and at other temperatures. This observation suggests the existence of spatially uniform valence band order near the pseudogap temperature. In addition, we observed periodic oscillations in the specular reflectivity from the sample surface that resemble thin film interference fringes, though no known film is present. These fringes are highly resonant, appear in all polarizations, and exhibit a period that depends on the location where the beam strikes the sample surface. We speculate that these fringes arise from interaction between some intrinsic valence band instability and extrinsic structural surface morphologies of the material. Our study supports the existence of some kind of $Q \sim 0$ broken symmetry state in Bi-2212 at intermediate temperatures, and calls for further study using a microfocused beam that could disentangle microscopic effects from macroscopic heterogeneities.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
