Wang Beilin, Guo Linhai, Ying Guopei, Duan Wenbu, Li Jian, Zeng Changgan
CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, and Department of Physics, University of Science and Technology of China, Hefei 230026, China.
International Center for Quantum Design of Functional Materials (ICQD), Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China.
Natl Sci Rev. 2025 Mar 21;12(6):nwaf105. doi: 10.1093/nsr/nwaf105. eCollection 2025 Jun.
Tunneling spectroscopy is a powerful tool for investigating the pairing mechanism of superconductors. However, the use of planar tunneling junctions to characterize Andreev bound states associated with unconventional superconductivity remains largely unexplored. Here, we report tunneling spectroscopy studies of normal-metal/superconductor planar junctions, leveraging the newly discovered LaAlO/KTaO(111) superconducting interface. We observe distinct spectroscopic behaviors for weak and strong tunneling barriers, controlled by the thickness of the LaAlO: when the barrier is weak, the metallic contact couples strongly with the interface superconductor, resulting in pronounced double peaks within the superconducting gap; when the barrier is strong, the in-gap peaks diminish and a softened full superconducting gap profile emerges. These observations, supported by theoretical calculations, pinpoint the presence of contact-induced Andreev bound states in planar junctions. This not only reveals the possibility of -wave superconductivity at the LaAlO/KTaO interface but also offers a universal approach to identifying the most sought-after superconducting states.
隧穿光谱学是研究超导体配对机制的有力工具。然而，利用平面隧穿结来表征与非常规超导相关的安德烈夫束缚态在很大程度上仍未得到充分探索。在此，我们报告了利用新发现的LaAlO/KTaO(111)超导界面进行的正常金属/超导体平面结的隧穿光谱学研究。我们观察到，由LaAlO的厚度控制的弱隧穿势垒和强隧穿势垒呈现出不同的光谱行为：当势垒较弱时，金属接触与界面超导体强烈耦合，在超导能隙内产生明显的双峰；当势垒较强时，能隙内的峰减弱，出现软化的完整超导能隙轮廓。这些观测结果在理论计算的支持下，确定了平面结中存在接触诱导的安德烈夫束缚态。这不仅揭示了LaAlO/KTaO界面处存在d波超导的可能性，还提供了一种识别最受追捧的超导态的通用方法。
