We study the conductance $g$ of an electron interferometer created in a two dimensional electron gas between a nanostructured contact and the depletion region induced by the charged tip of a scanning gate microscope. Using non-interacting models, we study the beating pattern of interference fringes exhibited by the images giving $g$ as a function of the tip position when a parallel magnetic field is applied. The analytical solution of a simplified model allows us to distinguish between two cases: (i) If the field is applied everywhere, the beating of Fabry-Pérot oscillations of opposite spins gives rise to interference rings which can be observed at low temperatures when the contact is open between spin-split transmission resonances. (ii) If the field acts only upon the contact, the interference rings cannot be observed at low temperatures, but only at temperatures of the order of the Zeeman energy. For a contact made of two sites in series, a model often used for describing an inversion-symmetric double-dot setup,
a pseudo-spin degeneracy is broken by the inter-dot coupling and a similar beating effect can be observed without magnetic field at temperatures of the order of the interdot coupling. Eventually, numerical studies of a quantum point contact with quantized conductance plateaus confirm that a parallel magnetic field applied everywhere or only upon the contact gives rises to similar beating effects between spin-split channel openings.
Probing topological Floquet states in graphene with ultrafast terahertz scanning tunneling microscopy
University of Bremen（不来梅大学）；Max Planck Institute for the Structure and Dynamics of Matter（马普物质结构与动力学研究所）；Paul Scherrer Institute（保罗谢尔研究所）；University of Fribourg（弗里堡大学）；The Flatiron Institute（_flatiron研究所）；Fritz Haber Institute of the Max Planck Society（马克斯·普朗克学会弗里茨·哈伯研究所）
Cryogen-free scanning gate microscope for the characterization of Si/Si$_{0.7}$Ge$_{0.3}$ quantum devices at milli-Kelvin temperatures
硅可以被同位素富集，允许制造高度相干的半导体自旋量子比特。然而，体硅的导带表现出六重谷简并，这可能会对硅量子器件的性能产生不利影响。到目前为止，硅中谷态的空间表征仍然有限。此外，需要用于探测功能电子器件中的谷态的技术。本文描述了一种用于在mK温度下表征Si/Si $_{0.7}$ Ge $_{0.3}$量子器件的无致冷剂扫描栅显微镜。该显微镜基于Pan-walker设计，具有粗定位压电堆栈和细扫描压电管。钨显微镜针尖连接到音叉上，用于主动控制针尖到样本的距离。为了降低脉冲管制冷机的振动噪声，我们利用主动和被动隔振机制，并实现了$\sim$ 2 nm的$z$均方根噪声。我们的显微镜被设计用于表征功能齐全的Si/Si $_{0.7}$ Ge $_{0.3}$量子器件。作为概念证明，我们使用显微镜来操纵Si量子点的电荷占据，为量子器件和材料的探索开辟了一系列可能性。
Electric Field Tuning of the Surface Band Structure of Topological Insulator Sb2Te3 Thin Films
用低温扫描隧道显微镜测量了外延Sb_2Te_3薄膜的表面态谱对外加栅电场的响应。费米能级的栅极相关位移和体载流子的屏蔽效应随膜厚的变化而变化。我们观察到的狄拉克点的薄膜薄于四五层，由于顶部和底部表面的耦合的间隙开口。此外，三个五层膜的顶面态带隙被发现是可调的背栅，表明在该系统中观察到拓扑相变的可能性。我们的结果很好地解释了一个有效的模型的三维拓扑绝缘体薄膜的结构反转不对称性，表明三个五层Sb 2 Te 3膜是拓扑非平凡的，属于量子自旋霍尔绝缘体类。
Evidence for a conical spin spiral state in the Mn triple-layer on W(001): spin-polarized scanning tunneling microscopy and first-principles calculations
Realization of Quantum Spin Hall State in Monolayer 1T'-WTe2
量子自旋霍尔（QSH）绝缘体是一种新型的二维量子态物质，在没有磁场的情况下具有量子化的霍尔电导，这是由于拓扑保护的无耗散边缘态桥接了由带反转和强自旋轨道耦合打开的能隙。通过使用角分辨光电子能谱（ARPES）和第一性原理计算研究外延生长的单层1 T '-WTe 2的电子结构，我们观察到清晰的拓扑带反转和带隙开放的特征，这是QSH态的标志。扫描隧道显微镜测量进一步证实了正确的晶体结构和体带隙的存在，并提供了证据的修改后的电子结构附近的边缘，这是一致的预期QSH绝缘体。我们的研究结果建立了单层1 T '-WTe 2作为一个强大的二维过渡金属二硫属化物（TMDC）材料家族中的一个新的类QSH绝缘体具有大的带隙。
