A Zero-loop Sagnac Interferometer for Probing Spontaneous Time Reversal Symmetry Breaking in Topological Superconductors

该提案用于购买建造零回路Sagnac干涉仪所需的设备，用于探测克尔旋转，灵敏度为亚µrad，空间分辨率为µm。近来二维材料的最大突破无疑是在扭曲双层石墨烯中发现了相关相和超导性。此外，去年刚刚报道了单层高温（Tc）超导体的成功隔离。受到这些发展的启发，我们的理论家同事马塞尔·弗兰兹提出了一个新的理论，预测第一个高温超导拓扑超导体可以从d波超导体的扭曲双层中出现。该理论预测，当两个单层d波超导体以45度的扭曲角堆叠时，两层之间的超导序参量会出现1/2的相位差。结果，超导体的总序参量获得手征对称性，高温超导体成为具有拓扑能隙的高温拓扑超导体。 在这里，我们建议通过制造高Tc超导体Bi 2Sr 2CaCu 2 O 8+的扭曲双层并用光探测其拓扑超导相来实验测试这一理论。根据该理论，时间反演对称性将在转变温度以下自发地破坏，这将引起极克尔效应。由于拓扑能隙比探测光的光子能量小得多，克尔旋转角预计会低于µrad。因此，我们计划建立一个国家的最先进的Sagnac干涉仪与克尔旋转的极端灵敏度（几十nrads）。该仪器将使我们能够展示第一个高温拓扑超导体，并解决该领域的一些开放的基本问题。我们在高温下实现拓扑超导性的新方法可能会为未来的拓扑量子计算带来新的机会。 在与同事的合作中，我们还将应用所提出的设备来探测其他低维系统中的边缘时间反演对称性破缺，例如扭曲双层石墨烯（Folk组），MBE生长的单层铁磁体，Fe 3GeTe 2（Zou群），HfNiSn中表面态沿沿着（111）方向（Aronson组），高熵磁性合金（Hallas组）和过渡金属二硫族化物异质结构，这是我自己的小组的兴趣。使用最先进的Sagnac干涉仪的经验将为我们的HQP提供极其宝贵的技能，这将有助于他们在学术界内外的职业生涯。

This proposal is for the purchase of equipment required to build a zero-loop Sagnac interferometer for probing Kerr rotation with a sub-µrad sensitivity and a µm spatial resolution. The biggest breakthrough in two-dimensional materials recently is inarguably the discovery of correlated phases and superconductivity in twisted bilayer graphene. In addition, the successful isolation of monolayer high-temperature (Tc) superconductors was just reported last year. Inspired by these developments, our theorist colleague, Marcel Franz, proposed a new theory predicting that the first high-Tc topological superconductor can emerge out of a twisted bilayer of d-wave superconductors. The theory predicts that when two monolayers of d-wave superconductors are stacked with a forty-five degree twist angle, a /2 phase difference arises in the superconducting order parameter between the two layers. As a result, the total superconducting order parameter acquires chiral symmetry and the high-Tc superconductor becomes a high-Tc topological superconductor with a topological gap. Here we propose to experimentally test this theory by fabricating twisted bilayers of a high-Tc superconductor, Bi2Sr2CaCu2O8+, and probing their topological superconducting phase with light. According to the theory, the time reversal symmetry will spontaneously break below the transition temperature, which will give rise to a Polar Kerr Effect. Since the topological gap is much smaller than the probe light's photon energy, the Kerr rotation angle is expected to fall below µrad. Therefore we plan to build a state-of-the-art Sagnac interferometer with an extreme sensitivity for Kerr rotation (tens of nrads). This instrument will allow us to demonstrate the first high-Tc topological superconductor, as well as resolve some open fundamental questions in the field. Our new approach to realizing topological superconductivity at high temperature might enable new opportunities for topological quantum computing in the future. In collaboration with colleagues, we will also apply the proposed equipment to probing the marginal time reversal symmetry breaking in other low-dimensional systems, such as the twisted bilayer graphene (Folk group), the MBE-grown monolayer ferromagnet, Fe3GeTe2 (Zou group), the surface state in HfNiSn along the (111) direction (Aronson group), high-entropy magnetic alloys (Hallas group), and transition-metal dichalcogenide heterostructures, which is of my own group's interest. The experience of working with the state-of-the-art Sagnac interferometer will provide our HQPs with extremely valuable skills which will help their careers both within and beyond academia.