Microscopic Coexistence of Superconductivity and Magnetism inBa1−xKxFe2As2

Abstract

It is widely believed that, in contrast to its electron-doped counterparts, the hole-doped compound Ba(1-x)K(x)Fe(2)As(2) exhibits a mesoscopic phase separation of magnetism and superconductivity in the underdoped region of the phase diagram. Here, we report a combined high-resolution x-ray powder diffraction and volume-sensitive muon spin rotation study of Ba(1-x)K(x)Fe(2)As(2) showing that this paradigm does not hold true in the underdoped region of the phase diagram (0≤x≤0.25). Instead we find a microscopic coexistence of the two forms of order. A competition of magnetism and superconductivity is evident from a significant reduction of the magnetic moment and a concomitant decrease of the magnetoelastically coupled orthorhombic lattice distortion below the superconducting phase transition.

Muon spin rotation study of magnetism and superconductivity in Ba(Fe1−xCox)2Bernhard1, Wang2, Nuccio3 et al. 2012Phys. Rev. B5422871View full textAdd to dashboardCite

“…Albeit, for Ba 1−x K x Fe 2 As 2 a recent study established that the macroscopic phase segregation does not occur in high-quality samples where the AF and superconducting orders truly coexist on the nanometer scale. 22 This suggests that the macroscopic phase segregation previously reported for Ba 1−x K x Fe 2 As 2 single crystals 18,19 is of chemical origin, likely due to a variation in the K content. 23 Even for the Ba(Fe 1−x Co x ) 2 As 2 system, which is rather well investigated thanks to the availability of sizable and fairly homogeneous single crystals, it remains to be investigated in detail how exactly the magnetic order evolves and disappears around optimum doping.…”

“…The relaxation rate of the oscillatory signal in the ZF-μSR spectrum of the Ba 1−x K x Fe 2 As 2 sample with x = 0.19 in Ref. 22 is indeed significantly smaller than the one of the Ba(Fe 1−x Co x ) 2 As 2 crystal at x = 0.045 which is in a similarly underdoped state with T c ≈ 0.5T c, max . Nevertheless, in both the K-and the Co-substituted samples the μSR precession frequency and thus the magnetic order parameter are only moderately reduced as long as the samples are not yet superconducting or remain strongly underdoped with T c 0.5T c, max .…”

“…60 Further information about the role of the Co-induced disorder in the suppression of the magnetism can be obtained from the comparison with the μSR data on the hole-doped Ba 1−x K x Fe 2 As 2 . 22 The substitution-induced disordering effects should be significantly weaker here since the K ions are incorporated on the Ba sites where they do not directly disturb the iron arsenide layers. The relaxation rate of the oscillatory signal in the ZF-μSR spectrum of the Ba 1−x K x Fe 2 As 2 sample with x = 0.19 in Ref.…”

“…Its oscillatory signal has a large amplitude and a small relaxation rate similar to that in previous μSR experiments. 22,56,57 The fit shown by the solid line has been obtained with the function…”

Visualizing the microscopic coexistence of spin density wave and superconductivity in underdoped NaFe1−xCoxAs

“…A key question here is whether the magnetic order and superconductivity can coexist microscopically or mutually exclude each other. So far the available experimental methods used to answer this question are either spatially averaged probes or local ones without control of probing position, thus a consensus is still lacking [3][4][5][6][7][8][9] . Experiments on various iron pnictide compounds have revealed at least three categories of behaviour.…”