标题： Bi$_2$Se$_3$薄膜在Ge(111)上外延生长的磁输运特性 显示英文标题

标题： Magnetotransport in Bi$_2$Se$_3$ thin films epitaxially grown on Ge(111)

摘要： 拓扑绝缘体（TIs）如Bi$_2$Se$_3$是一类具有拓扑保护表面态的材料，在这种材料中自旋-动量锁定可能实现自旋极化和缺陷容错传输。 在本工作中，我们在锗上实现了Bi$_2$Se$_3$薄膜的外延生长，锗是微电子学中的关键材料。 锗在电子自旋方面也表现出有趣的特性，例如在室温下自旋扩散长度可达几微米。 通过在锗上生长Bi$_2$Se$_3$，我们旨在结合Ge的长自旋扩散长度与Bi$_2$Se$_3$表面的自旋-动量锁定。 我们首先使用电子衍射和X射线衍射以及原子力显微镜对Bi$_2$Se$_3$薄膜进行了全面的结构分析。 然后，低温下的磁输运测量显示了由于拓扑保护表面态中的二维输运而导致的弱反局域化特征，这是Bi$_2$Se$_3$的结果。 有趣的是，磁输运测量还表明，通过偏置电压或施加的磁场，导电通道可以在Bi$_2$Se$_3$薄膜和其下方的Ge层之间进行调节。 这一结果表明，Bi$_2$Se$_3$/Ge 结是调节拓扑绝缘体和半导体界面之间自旋相关现象的有前途的候选结构。 显示英文摘要

摘要： Topological insulators (TIs) like Bi$_2$Se$_3$ are a class of material with topologically protected surface states in which spin-momentum locking may enable spin-polarized and defect-tolerant transport. In this work, we achieved the epitaxial growth of Bi$_2$Se$_3$ thin films on germanium, which is a key material for microelectronics. Germanium also exhibits interesting properties with respect to the electron spin such as a spin diffusion length of several micrometers at room temperature. By growing Bi$_2$Se$_3$ on germanium, we aim at combining the long spin diffusion length of Ge with the spin-momentum locking at the surface of Bi$_2$Se$_3$. We first performed a thorough structural analysis of Bi$_2$Se$_3$ films using electron and x-ray diffraction as well as atomic force microscopy. Then, magnetotransport measurements at low temperature showed the signature of weak antilocalization as a result of two-dimensional transport in the topologically protected surface states of Bi$_2$Se$_3$. Interestingly, the magnetotransport measurements also point out that the conduction channel can be tuned between the Bi$_2$Se$_3$ film and the Ge layer underneath by means of the bias voltage or the applied magnetic field. This result suggests that the Bi$_2$Se$_3$/Ge junction is a promising candidate for tuning spin-related phenomena at interfaces between TIs and semiconductors.