Bandwidth-Control Orbital-Selective Delocalization of 4f Electrons in Epitaxial Ce Films

Result of the Month

The 4f-electron delocalization plays a key role in the low-temperature properties of rare-earth metals and intermetallics, and it is normally realized by the Kondo coupling between 4f and conduction electrons. Due to the large Coulomb repulsion of 4f electrons, the bandwidth-control Mott-type delocalization, commonly observed in d-electron systems, is difficult in 4f-electron systems and remains elusive in spectroscopic experiments. Here we demonstrate that the bandwidth-control orbital-selective delocalization of 4f electrons can be realized in epitaxial Ce films by thermal annealing, which results in a metastable surface phase with reduced layer spacing. The quasiparticle bands exhibit large dispersion with exclusive 4f character near Γ and extend reasonably far below the Fermi energy, which can be explained from the Mott physics. The experimental quasiparticle dispersion agrees well with density-functional theory calculation and also exhibits unusual temperature dependence, which could arise from the delicate interplay between the bandwidth-control Mott physics and the coexisting Kondo hybridization. Our work opens up the opportunity to study the interaction between two well-known localization-delocalization mechanisms in correlation physics, i.e., Kondo vs Mott, which can be important for a fundamental understanding of 4f-electron systems.

Figure Description: Electronic structure of a thick Ce film at 20 K after progressive post-growth annealings from ~370 to ~540 K. a Three representative ARPES spectra at different stages of annealings: disordered Ce film (P0), ordered Ce films at intermediate annealing temperature (P1), and at high annealing temperature (P2). b Energy distribution curves (EDCs) at the Γ point for these three phases. The insets are the corresponding RHEED images. c Cartoons illustrating the proposed origin of the different electronic structures. The reduction of the interlayer spacing in P2 is exaggerated.

MBE Growth & Annealing

Ce films were grown on top of epitaxial graphene layers at a temperature of approx. 100 °C and at a rate of 2 Å/min using a high-temperature effusion cell of a Lab10 MBE. The Ce films were sequentially annealed from 370 to 540 K.

ARPES Measurements

Samples were immediately transferred in UHV from the MBE chamber to a connected ARPES Lab equipped with a DA30-L analyser and a VUV5k He lamp. Measurements were conducted at a sample temperature of 20 K and at an operating pressure of 2.3 × 10−10 mbar. The pass energy was set to 10 eV yielding approx. 15 meV energy resolution.


Yi Wu, Yuan Fang, Peng Li, Zhiguang Xiao, Hao Zheng, Huiqiu Yuan, Chao Cao, Yi-feng Yang, Yang Liu


  • Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou, China.

        Yi Wu, Yuan Fang, Peng Li, Zhiguang Xiao, Hao Zheng, Huiqiu Yuan, Yang Liu

  • Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou, China.

       Huiqiu Yuan, Yang Liu

  • Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China.

       Huiqiu Yuan, Yang Liu

  • Department of Physics, Hangzhou Normal University, Hangzhou, China.

       Chao Cao

  • Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China.

       Yi-feng Yang

  • School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, China.

       Yi-feng Yang

  • Songshan Lake Materials Laboratory, Dongguan, Guangdong, China.

        Yi-feng Yang

Corresponding Authors

Yi-feng Yang:

Yang Liu:

Publicaton: Wu, Y., Fang, Y., Li, P. et al. Bandwidth-control orbital-selective delocalization of 4f electrons in epitaxial Ce films. Nat Commun 12, 2520 (2021).