磁性/拓扑范德华异质结的外延生长与超导物性研究

EPITAXIAL GROWTH AND SUPERCONDUCTING PROPERTIES OF MAGNETIC MATERIALS AND TOPOLOGICAL VAN DER WAALS HETEROJUNCTIONS

张猛

11649102

硕士

材料物理与化学

王干

2018-05-30

2018-07-04

哈尔滨工业大学

深圳

近些年来，有关拓扑表面电子态的研究已经成为凝聚态物理以及材料科学领域的一个热点研究方向。自从拓扑绝缘体（TI）被理论预测及发现以来，有关其研究的一个重要方向就是研究拓扑表面态与磁有序态的相互作用机制。比如拓扑绝缘体与磁性材料异质结产生的超导现象引起了很多研究人员的关注。在本文中，通过分子束外延生长（MBE）方法生长Bi2Te3/FeTe 这样一个拓扑绝缘体/磁性材料异质结结构，通过反射式高能电子衍射仪（RHEED），扫描隧道显微镜测试（STM）、表征样品质量，并通过低温输运测试，分析不同生长条件对异质结超导转变温度等性质的影响。本文主要内容包括：探索Bi2Te3 和FeTe 薄膜的MBE 生长条件，通过梯度改变蒸发的温度和生长基底温度，结合RHEED 测试，找出了生长优质薄膜的条件，并通过输运测试，探索出实现异质结超导的条件，为以后的异质结超导研究打下基础。同时分析了在各种不合适条件下样品的生长模式，为之后超导异质结的研究积攒了经验。实验结果显示生长时候的基底温度和Fe 与Te 蒸发源的温度都会影响到异质结是否超导，其中Fe 与Te 的比例尤为重要，并不是好的FeTe 薄膜与Bi2Te3 生长就会超导，超导的发生需要一个合适的比例。而在超导情况下，这种结构的异质结超导转变温度跟Bi2Te3 的生长厚度有很大关系，Bi2Te3 的厚度越厚测量到的超导转变温度越低。此外，为理解和解释超导机理，还设计了一些实验，希望通过实验和理论手段来理解异质结超导发生的位置和输运现象。

In recent years, the study on the electronic states of topological surfaces has become a popular research direction in the field of condensed matter physics and materials science. Since the Topology Insulator (TI) was theoretically predicted and discovered, a significant direction in its research has been the study of the interaction mechanism between the topological surface state and the magnetic ordered state. For instance, superconductivity caused by heterojunctions between topological insulator and magnetic material has aroused the attention of many researchers.In this paper, Bi2Te3/FeTe with a topological insulator/magnetic heterojunction structure was grown by molecular beam epitaxial growth (MBE) method. Through a reflective high energy electron diffractometer (RHEED), the tunneling microscopy (STM) was scanned to characterize samples quality. Also, through low-temperature transport tests, the effect of different growth conditions on the properties of superconducting heterojunction like transition temperature was analyzed.The main contents of this paper are as follows: exploring the MBE growth conditions of Bi2Te3 and FeTe thin films, changing the evaporation temperature and the growth substrate temperature by gradients, combining with the RHEED test, finding out the conditions for the growth of high quality thin films, and exploring the condition of realizing heterojunction superconductivity through transport testing and laying the foundation for future research on heterojunction superconductivity. At the same time, the growth mode of the sample under various unsuitable conditions was analyzed, which accumulated experience for the later research on superconducting heterojunction. The experimental results showed that the substrate temperature during the growth and the temperature of the evaporation source of Fe and Te both had an effect on the superconductivity of the heterojunction. The ratio of Fe to Te was particularly important. The occurrence of superconductivity was not produced by good FeTe film and Bi2Te3 growth, but a proper ratio of Fe to Te. In the case of superconductivity, the heterojunction superconducting transition temperature of this structure is closely related to the growth thickness of Bi2Te3. The larger the thickness of Bi2Te3, the lower the superconducting transition temperature.In addition, to understand and explain the mechanism of superconductivity, some experiments were designed, hoping to understand the position and transport phenomenon of heterojunction superconductivity through experimental and theoretical approaches.

界面超导 分子束外延生长 磁性材料 拓扑绝缘体 异质结

interface superconductor molecular beam epitaxy topological insulator magnetic material heterojunction

中文

联合培养

哈尔滨工业大学

张猛. 磁性/拓扑范德华异质结的外延生长与超导物性研究[D]. 深圳. 哈尔滨工业大学,2018.