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Dimensionality Tuning of Heavy-Fermion States in Ultrathin CeSi2 Films

Yi Wu1,2,*, Weifan Zhu1,2,*, Teng Hua1,2,*, Yuan Fang3,*, Yanan Zhang1,2, Jiawen Zhang1,2, Yanen Huang1,2, Hao Zheng1,2, Shanyin Fu1,2 et al.

Xinying Zheng1,2, Zhengtai Liu4, Mao Ye4, Ye Chen1,2, Tulai Sun5,†, Michael Smidman1,2, Johann Kroha6,7, Chao Cao1,2,8, Huiqiu Yuan1,2,8,‡, Frank Steglich1,2,9, Hai-Qing Lin1,8, and Yang Liu1,2,8,§

  • *These authors contributed equally to this paper.
  • †Contact author: tlsun2020@zjut.edu.cn
  • ‡Contact author: hqyuan@zju.edu.cn
  • §Contact author: yangliuphys@zju.edu.cn
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Phys. Rev. X 16, 011053 – Published 10 March, 2026

DOI: https://doi.org/10.1103/fyjf-rwdq

Abstract

Dimensionality tuning is an important method to modify the electronic states of quantum materials. However, the mechanism of such tuning in heavy fermion systems and its connection with transport properties remain largely unexplored. Here by combining molecular beam epitaxy, in situ angle-resolved photoemission spectroscopy and transport measurements, we study the electronic states of the heavy-fermion compound CeSi2 as a function of film thickness. In three-dimensional thick films, our measurements reveal a dispersive Kondo peak at the Fermi level (EF) and satellite peaks originating from crystal electric field (CEF) excitations, characteristic of heavy-fermion systems. For two-dimensional ultrathin films, the CEF satellites are largely suppressed while the ground-state Kondo peak at EF remains strong, although it develops at lower temperatures. Simultaneously, the maximum temperature Tmax of the magnetic resistivity, ρm(T), changes from ≈100  K in thick films to ≈35  K in ultrathin films. This can be attributed to the dimensionality-driven reduction of CEF excitations during the Kondo process, in good agreement with spectroscopic results. Our work provides direct insight to understand the quantum confinement effects on strongly correlated 4f-electron systems and opens up new opportunities to explore emergent phenomena in two-dimensional heavy-fermion materials.

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Popular Summary

Understanding how the heavy-fermion state evolves from three to two dimensions is a fundamental question in strongly correlated physics, yet it remains largely unexplored because most prototypical materials lack a direct two-dimensional counterpart. We addressed this by using molecular beam epitaxy to grow films of the canonical heavy-fermion compound CeSi2 with controllable thicknesses and studying them via in situ angle-resolved photoemission spectroscopy. Our measurements reveal that decreasing the film thickness leads to a clear suppression of crystal electric field excitations, which in turn reduces the effective Kondo energy. We found that while the Kondo peak at the Fermi level remains strong in the two-dimensional limit, it develops at lower temperatures, consistent with the evolution in the magnetic resistivity. These results show that enhanced electron correlations in two-dimensional heavy-fermion metals are intimately connected to this suppression of electronic excitations. Our findings establish CeSi2 as a platform for exploring emergent phenomena like ferromagnetic quantum criticality in reduced dimensions.

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Phys. Rev. X 16, 011053– Published 10 March, 2026
  • Received 22 April 2025
  • Revised 22 December 2025
  • Accepted 5 February 2026
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