Interplay of superconductivity and d-f correlation in CeFeAs_(1-x)P_xO_(1-y)F_y

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 T K ～ 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 CeFeAsO 1-y F y (y = 0 and 0.05). This P/As-doping in CeFeAsO serves as an effective controlling parameter which leads to two magnetic critical points, x c1 0.4 and x c2 0.92, associated with suppression of 3d and 4f magnetism, respectively. We also observe a turning point of AFM-FM ordering of Ce 3+ moment at x c3 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 x c1 . We continue to investigate CeFeAs 1-x P x O 0.95 F 0.05 . With the separation of x c1 and x c3 , 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.     

Low-Temperature Properties of CePt_3P Tuned by Magnetic Field

We present low-temperature magnetization, magnetoresistance and specific heat measurements on the Kondo lattice compound CePt_3P under applied magnetic fields up to 9.0 T. At zero field, CePt_3P exhibits a moderately enhanced Sommerfeld coefficient of electronic specific heat γCe=86 mJ/mol·K~2 as well as two successive magnetic transitions of Ce 4f moments: an antiferromagnetic ordering at T_(N_1) = 3.0 K and a spin reorientation at T_(N_2)=1.9 K. The value of T_(N_1) shifts to lower temperature as magnetic field increases, and it is ultimately suppressed around B_c ～3.0 T at 1.5 K. No evidence of non-Fermi liquid behavior is observed around B_c down to the lowest temperature measured. Moreover, γ decreases monotonously with increasing the magnetic field. On the other hand, the electrical resistivity shows an anomalous temperature dependence ρ∝T~n with the exponent n decreasing monotonously from ～2.6 around B_c down to ～1.7 for B = 9.0 T. The T-B phase diagram constructed from the present experimental results of CePt_3P does not match the quantum criticality scenario of heavy fermion systems.     

Interplay of superconductivity and d-f correlation in CeFeAslPOl_yFy

The recent discovery of high-temperature superconductivity in iron-based pnictides （chalcogenides） not only trig- gers 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 corelated 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 CeFeAsOl_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, Xcl -- 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 Xcl. We continue to investigate CeFeAsl-xPxO0.95Fo.os. With the separation of xcl 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.     

Superconductivity and Transport Properties in Th and F Codoped Sm1-xThxFeAsO1-yFy

A series of Th and F co-doped superconductors Sm1-xThxFeAsO1-yFy are synthesized and the variation of superconductivity with the doping level is investigated. At the fixed Th doping level x = 0.1, the superconducting transition temperature Tc increases monotonically with F content, and finally Tc reaches a maximum of about 55K around y = 0.1, and saturates for even more F content the normal state thermopower increases monotonically with ＇overdoped＇ regime is not observed and possible explanation （y = 0.15）. Similar to the SmFeAsO1-y Fy system, the doping level. However the decrease of Tc in the is discussed.