中国物理B ›› 2026, Vol. 35 ›› Issue (6): 67103-067103.doi: 10.1088/1674-1056/ae0b45

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Moiré superlattice on the surface of Sm films driven by surface valence transition

Jianzhou Bian(边建州)1,†, Hao Zheng(郑浩)2,†, Yonghao Liu(刘永昊)3, Zongxiu Wu(邬宗秀)3, Yuan Zheng(郑远)3, Yi Yin(尹艺)3,‡, Yang Liu(刘洋)2,§, and Xiaofeng Xu(许晓峰)1,¶   

  1. 1 School of Physics, Zhejiang University of Technology, Hangzhou 310023, China;
    2 Center for Correlated Matter and School of Physics, Zhejiang University, Hangzhou 310058, China;
    3 Zhejiang Province Key Laboratory of Quantum Technology and Device, School of Physics, Zhejiang University, Hangzhou 310027, China
  • 收稿日期:2025-05-27 修回日期:2025-08-25 接受日期:2025-09-25 发布日期:2026-06-05
  • 通讯作者: Yi Yin, Yang Liu, Xiaofeng Xu E-mail:yiyin@zju.edu.cn;yangliuphys@zju.edu.cn;xuxiaofeng@zjut.edu.cn
  • 基金资助:
    Project supported by the National Key Research and Development Program of China (Grant Nos. 2022YFA1403202 and 2022YFA1402200), the National Natural Science Foundation of China (Grant Nos. 12174331 and 12274369), and the Zhejiang Provincial Natural Science Foundation of China (Grant No. LZ25A040003).

Moiré superlattice on the surface of Sm films driven by surface valence transition

Jianzhou Bian(边建州)1,†, Hao Zheng(郑浩)2,†, Yonghao Liu(刘永昊)3, Zongxiu Wu(邬宗秀)3, Yuan Zheng(郑远)3, Yi Yin(尹艺)3,‡, Yang Liu(刘洋)2,§, and Xiaofeng Xu(许晓峰)1,¶   

  1. 1 School of Physics, Zhejiang University of Technology, Hangzhou 310023, China;
    2 Center for Correlated Matter and School of Physics, Zhejiang University, Hangzhou 310058, China;
    3 Zhejiang Province Key Laboratory of Quantum Technology and Device, School of Physics, Zhejiang University, Hangzhou 310027, China
  • Received:2025-05-27 Revised:2025-08-25 Accepted:2025-09-25 Published:2026-06-05
  • Contact: Yi Yin, Yang Liu, Xiaofeng Xu E-mail:yiyin@zju.edu.cn;yangliuphys@zju.edu.cn;xuxiaofeng@zjut.edu.cn
  • Supported by:
    Project supported by the National Key Research and Development Program of China (Grant Nos. 2022YFA1403202 and 2022YFA1402200), the National Natural Science Foundation of China (Grant Nos. 12174331 and 12274369), and the Zhejiang Provincial Natural Science Foundation of China (Grant No. LZ25A040003).

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摘要： Rare earth (RE) metals exhibit unique mixed-valence behavior due to their 4f electronic configurations. In this study, we investigate the surface electronic structure and valence-mixing phenomena in samarium (Sm) films using molecular beam epitaxy (MBE), scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT). A natural moiré superlattice emerges on the Sm film surface as a result of lattice mismatch between the surface divalent Sm$^{2+}$ and bulk trivalent Sm$^{3+}$ layers. ARPES reveals the flat f electron bands corresponding to Sm$^{3+}$ and Sm$^{2+}$ states, particularly demonstrating the partial coexistence of bulk Sm$^{2+}$ flat bands. The dispersive s-d electron bands and surface-condition-induced band shifts are observed and analyzed through both STM and ARPES measurements. Our work provides direct evidence for the formation of a moiré pattern on the surface of Sm films due to its unique surface valence transition, thus paving the way for a new method to generate moiré superlattices in correlated 4f-electron systems.

关键词: samarium, mixed valence, angle-resolved photoelectron spectroscopy, scanning tunneling microscopy

Abstract: Rare earth (RE) metals exhibit unique mixed-valence behavior due to their 4f electronic configurations. In this study, we investigate the surface electronic structure and valence-mixing phenomena in samarium (Sm) films using molecular beam epitaxy (MBE), scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT). A natural moiré superlattice emerges on the Sm film surface as a result of lattice mismatch between the surface divalent Sm$^{2+}$ and bulk trivalent Sm$^{3+}$ layers. ARPES reveals the flat f electron bands corresponding to Sm$^{3+}$ and Sm$^{2+}$ states, particularly demonstrating the partial coexistence of bulk Sm$^{2+}$ flat bands. The dispersive s-d electron bands and surface-condition-induced band shifts are observed and analyzed through both STM and ARPES measurements. Our work provides direct evidence for the formation of a moiré pattern on the surface of Sm films due to its unique surface valence transition, thus paving the way for a new method to generate moiré superlattices in correlated 4f-electron systems.

Key words: samarium, mixed valence, angle-resolved photoelectron spectroscopy, scanning tunneling microscopy

中图分类号:  (Strongly correlated electron systems; heavy fermions)

  • 71.27.+a
79.60.-i (Photoemission and photoelectron spectra) 68.37.Ef (Scanning tunneling microscopy (including chemistry induced with STM)) 73.20.At (Surface states, band structure, electron density of states)