Interplay of superconductivity and d—f correlation in CeFeAs1−xPxO1−yFy.

The recent discovery of high-temperature superconductivity in iron-based pnictides (chalcogenides) not only triggers tremendous enthusiasm in searching for new superconducting materials, but also opens a new avenue to the study of the Kondo physics. CeFeAsO is a parent compound of the 1111-type iron-based superconductors. It shows 3d-antiferromagnetic (AFM) ordering below ∼ 139 K and 4f-AFM ordering below ∼ 4 K. On the other hand, the phosphide CeFePO is a ferromagnetically correlated heavy-fermion (HF) metal with Kondo scale TK ∼ 10 K. These properties set up a new platform for research of the interplay among magnetism, Kondo effect, and superconductivity (SC). In this review, we present the recent progress in the study of chemical pressure effect in CeFeAsO1−yFy (y = 0 and 0.05). This P/As-doping in CeFeAsO serves as an effective controlling parameter which leads to two magnetic critical points, xc1 ≃ 0.4 and xc2 ≃ 0.92, associated with suppression of 3d and 4f magnetism, respectively. We also observe a turning point of AFM-FM ordering of Ce3+ moment at xc3 ≃ 0.37. The SC is absent in the phase diagram, which is attributed to the destruction to Cooper pair by Ce-FM fluctuations in the vicinity of xc1. We continue to investigate CeFeAs1−xPxO0.95F0.05. With the separation of xc1 and xc3, this chemical pressure results in a broad SC region 0≤ x ≤ 0.53, while the original HF behavior is driven away by 5% F− doping. Different roles of P and F dopings are addressed, and the interplay between SC and Ce-4f magnetism is also discussed. [ABSTRACT FROM AUTHOR]