Probing the local 4f-orbital symmetry in heavy fermion systems by linearly polarized <i>angle-resolved</i> core-level hard x-ray photoemission spectroscopy

Ground-state (GS) orbital symmetry determined by the local effective crystalline electric fields (CEF) in strongly correlated electron systems play crucial roles in their functional properties such as superconductivity and multipolar ordering. We have found that the CEF-split GS 4f-orbital symmetry can be probed by linear dichroism (LD) in angle-resolved core d-level hard x-ray photoemission owing to the selecion rules in the optical process [1]. We have applied this technique to Ce, Pr, and Yb-based heavy fermion systems, where the Γ₇ states with Jz = ±3/2 and the Γ₈ states in the CEF-split GS 4f symmetry have been established for tetragonal YbRh₂Si₂ [2] and cubic YbB₁₂ [3]. Mutually different LDs reflecting the different orbital symmetry have been seen for cubic PrBe₁₃, PrB₆, and PrIr₂Zn₂₀ [4,5]. This technique has also revealed the CEF-split GS 4f wave functions for a pressure-induced superconductor CeCu₂Ge₂ [6].

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[4] S. Hamamoto et al., J. Phys. Soc. Jpn. 86, 123703 (2017).
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[6] H. Aratani et al., Phys. Rev. B 98, 121113(R) (2018).