Homogeneous vs. inhomogeneous coexistence of magnetic order and superconductivity probed by NMR in Co- and K-doped iron pnictides

Abstract

In Ba(Fe0.95Co0.05)2As2 all of the 75 As NMR intensity at the paramagnetic resonance position vanishes abruptly below T onset SDW = 56 K, indicating that magnetic (spin density wave) order is present in all of the sample volume, despite bulk superconductivity below Tc=15 K. The two phases thus coexist homogeneously at the microscopic scale. In Ba0.6K0.4Fe2As2, on the other hand, the signal loss below T onset SDW ≃75 K is not complete, revealing that magnetic order is bound to finite-size areas of the sample, while the remaining NMR signal shows a clear superconducting response below Tc = 37 K. Thus, the two phases are not homogeneously mixed, at least for this potassium concentration. For both samples, spatial electronic and/or magnetic inhomogeneity is shown to characterize the NMR properties in the normal state.

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

“…A true coexistence and competition between short-ranged but bulk AF order and superconductivity has been established in underdoped samples of Sm-1111 11,12 and especially in single crystals of Ba(Fe 1−x Co x ) 2 As 2 . [13][14][15][16] Such a coexistence was not observed in La-1111. 17 Moreover, in Ba 1−x K x Fe 2 As 2 (Refs.…”

Structural chemistry of superconducting pnictides and pnictide oxides with layered structures

“…14) is still controversial. Findings from 57 Fe-Mössbauer spectroscopy gave evidence of homogeneous co-existence, while 75 As-NMR [106] and mSR [107] data indicated mesoscopic phase separation in magnetic and superconducting fractions. On the other hand, homogeneous co-existence is generally accepted in the Co-doped system Ba(Fe 1Àx Co x ) 2 As 2 [108] (see below).…”

Quasiparticle states around a nonmagnetic impurity in electron-doped iron-based superconductors with spin-density-wave order

“…Furthermore, in some of the iron-based materials the SC and SDW orders are proposed to coexist in the underdoped regime. [18][19][20][21][22][23][24][25][26] The issue is still a subject of discussion and we anticipate that the impurity effect could provide additional signatures for the coexistence of these two orders.…”