Phase diagram ofCeFeAs1−xPxOobtained from electrical resistivity, magnetization, and specific heat measurements

Abstract

We performed a systematic study on the properties of CeFeAs1−xPxO (0 ≤ x ≤ 1) by electrical resistivity, magnetization and specific heat measurements. The c-axis lattice constant decreases significantly with increasing P content, suggesting a remarkable chemical pressure. The Fe-3d electrons show the enhanced metallic behavior upon P-doping and undergo a magnetic quantum phase transition around x ≈ 0.4. Meanwhile, the Ce-4f electrons develop a ferromagnetic order near the same doping level. The ferromagnetic order is vanishingly small around x = 0.9. The data suggest a heavy-fermion-like behavior as x ≥ 0.95. No superconductivity is observed down to 2 K. Our results show the ferromagnetic ordered state as an intermediate phase intruding between the antiferromagnetic bad metal and the nonmagnetic heavy fermion metal and support the cerium-containing iron pnictides as a unique layered Kondo lattice system.

Ferromagnetism and superconductivity in CeFeAs1−xPxO (Jesche1, Förster2, Spehling3 et al. 2012Phys. Rev. B

“…Instead a crossover to ferromagnetic (FM) ordering of Ce was reported at a critical concentration of x ≈ 40%, where the AFM ordering of Fe vanishes. 16 In contrast or in addition to this results we have found the following: (1) long-range FM ordering coexisting with superconductivity in a small homogeneity range around x = 30%, (2) evidence against a quantum-critical scenario, (3) static AFM ordering of Fe moments in the absence of structural distortion, and (4) a clear electron spin resonance (ESR) signal connected to ferromagnetism.Polycrystalline and single crystalline materials were syn- …”

“…In this sense CeFeAs 1−x P x O presents a unique situation because of the following: First, replacing As with P "usually" results in SC as shown for AFe 2 As 2 [A = Ca, 9 Ba, 10 Sr, 9 Eu 11 ] and RFeAsO [R = La, 5 Sm 12 ], and second, CeFeAsO becomes superconducting when substituting Fe with Co 13 or O with F 14 and also by inducing oxygen vacancies. 2 But combining P doping with R = Ce among the RFeAsO compounds results in exceptional behavior: The Fe ordering is suppressed, as shown by de la Cruz et al 15 and Luo et al, 16 however, superconductivity had not yet been observed in CeFeAs 1−x P x O. Instead a crossover to ferromagnetic (FM) ordering of Ce was reported at a critical concentration of x ≈ 40%, where the AFM ordering of Fe vanishes.…”

“…22 x > 30% and the absence of SC in these samples, we conclude a competing character of both effects (see the phase diagram in Fig. 4 and Luo et al 16 ). However, the situation is more subtle than a simple competition of local moment ferromagnetism and conduction band superconductivity since the observed behavior of CeFeAs 0.70 P 0.30 O is significantly different from most superconducting iron pnictides already well above the Curie temperature of Ce, as we will show below.…”

The orbital characters of low-energy electronic structure in iron-chalcogenide superconductor K x Fe2−y Se2

“…While the parent compounds of most iron-based superconductors are metallic [2][3][4], the parent compound of K x Fe 2−y Se 2 superconductor is found to be either insulating or semiconducting [5][6][7][8][9]. The insulating parental phase even exhibits certain Mott-insulator signatures, and it is phase separated from the superconducting phase in the K x Fe 2−y Se 2 superconductor at a mesoscopic scale [7,10].…”

“…Since the low-energy electronic *Corresponding author (email: dlfeng@fudan.edu.cn) structures of the iron-based superconductors are dominated by multiple 3d orbitals [18][19][20], the orbital degree of freedom is known to play an important role in the superconductivity of iron-based superconductors. For example, our recent ARPES study on BaFe 2 (As 1−x P x ) 2 indicates that the nodal superconducting gap there is likely induced by the strong mixing of the d z 2 orbital into a hole-like band [21]. Therefore, to comprehend the unique properties of K x Fe 2−y Se 2 , one needs to determine its low-energy electronic structure, particularly the orbital characters.…”