Single-crystal superconducting Al thin film with high crystallinity and ultra-low interface roughness in Al2O3/Al/sapphire heterostructure for quantum computing
Yen-Hsun Glen Lin1*, Lawrence Boyu Young1, Li-Shao Chiang2, Hsien-Wen Wan1, Yi-Ting Cheng1, Chia-Hung Hsu3, Juhn-Jong Lin4, Che-Te Liang1, Yen-Hsiang Lin5, Jueinai Kwo5, Minghwei Hong1,2
1Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan
2Graduate Institute of Electronics Engineering, National Taiwan University, Taipei, Taiwan
3National Synchrotron Radiation Research Center, Hsinchu, Taiwan
4Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
5Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
* Presenter:Yen-Hsun Glen Lin,
Superconducting qubit has been the major platform for quantum computing. Despite the tremendous research efforts in both academia and industry, decoherence of quantum states due to dielectric loss remains a great challenge. The dielectric loss process mainly originated from the material imperfection of the superconducting thin films and interfaces between superconducting films and adjacent layers (substrate, air).
In this work, single crystal superconducting aluminum (Al) films were grown on sapphire substrates with thicknesses down to 3 nm. The Al layer was protected by an in-situ deposited Al2O3 layer without sacrificing the underlying Al film. The samples exhibited single crystal Al structure and very high crystallinity with record-low full-width at half-maximum rocking curves of 0.015o in synchrotron radiation X-ray diffraction study. The sample surfaces showed extremely low surface roughness of 0.1-0.2 nm by atomic force microscope. The high crystallinity and atomically flat surface suggested the well-controlled growth process of the Al films. Superconductivity was obtained in the Al films down to 3 nm, suggesting the feasibility of the superconducting devices using these single crystal ultra-thin superconducting films.

Keywords: Single crystal, Superconductor, Aluminum, Quantum Computing