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拓扑材料近年来得到了飞速的发展，利用铁磁材料对其进行磁近邻作为通向拓扑量子计算道路中的重要一环，持续吸引着凝聚态物理学界的关注. 本实验利用电子束蒸镀的手段在二维拓扑绝缘体InAs/GaInSb双量子阱表面生长铁磁绝缘体硫化铕（EuS），形成铁磁绝缘体/二维拓扑绝缘体（EuS/InAs/GaInSb）异质结构并制作霍尔器件，在低温下进行了系统的输运测量. 实验中发现，随着InAs中电子波函数的空间分布趋近EuS，EuS对其的磁近邻效应逐渐增强. 表现为霍尔器件在垂直磁场下的奇宇称磁阻的斜率逐渐增大，零场附近的正磁阻会向负磁阻转变，同时，平行磁场下的负磁阻效应亦会随之变强．结合电阻-温度曲线在低温段（低于20K）符合近藤效应的电阻上升行为，本文分析并得出InAs中电子气在磁场下的负磁阻可以解释为由近藤效应而引起的结论. 综合实验数据和分析，本工作给出了InAs/GaInSb中电子被EuS磁近邻的输运证据．
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关键词:
- 铁磁绝缘体/半导体异质结 /
- 拓扑绝缘体 /
- 磁电阻效应 /
- 自旋电子学
Magnetic proximity effects (MPE) are crucial for topological quantum devices because they enable control of boundary states between a ferromagnetic insulator and a topological insulator. The InAs/GaInSb double quantum well system—especially when combined with a superconductor and influenced by MPE—shows promise for producing topological qubits. Nonetheless, researchers still debate the exact strength of the MPE between europium sulfide (EuS) and InAs.
To directly probe the MPE, this work focuses on a EuS/InAs/GaInSb heterostructure. The heterostructure was fabricated by depositing EuS onto the passivated surface of a Hall bar formed from an InAs/GaInSb double quantum well, utilizing an electron beam evaporation system. Structural analysis using Reflection High-Energy Electron Diffraction and magnetic measurements revealed that, although the resulting EuS thin films were polycrystalline, they nonetheless displayed desired magnetic properties, making them suitable for further study of MPE phenomena.
Low-temperature magnetoresistance measurements on the fabricated Hall bar revealed several key phenomena that collectively provide evidence for the MPE. Application of a positive gate voltage caused the electron wavefunction within the InAs layer to shift toward the EuS interface, thereby enhancing the MPE. Under a perpendicular magnetic field, the magnetoresistance exhibited an increasing slope for the odd-parity component. Additionally, a transition from positive to negative magnetoresistance near zero field was observed. When an in-plane magnetic field was applied, a gate-enhanced negative magnetoresistance emerged. Hysteretic magnetoresistance, corresponding to the reversal of EuS magnetization, was also detected during these measurements.
The resistance-temperature curve for the heterostructure displayed a pronounced upturn at low temperatures. This behavior was well described by the Kondo model, indicating the presence of exchange coupling between InAs electrons and the localized magnetic moments of EuS near the interface. Such coupling is a strong indicator of the magnetic proximity effect at work in the system.
These findings collectively demonstrate the existence of a gate-tunable MPE in the EuS/InAs/GaInSb heterostructure. The ability to control the MPE through gate voltage establishes this heterostructure as a compelling platform for the exploration of proximity-induced magnetism. Furthermore, these results underscore the potential applications of such systems in the development of spin-based electronic devices and highlight their significance for future research in topological quantum computing.-
Keywords:
- ferromagnetic insulator/semiconductor heterostructure /
- topological insulator /
- magnetoresistance /
- spintronics
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