Uniaxial pressure effect on structural and magnetic phase transitions in NaFeAs and its comparison with as-grown and annealed BaFe2As2

Abstract

We use neutron scattering to study the effect of uniaxial pressure on the tetragonal-toorthorhombic structural (Ts) and paramagnetic-to-antiferromagnetic (TN ) phase transitions in NaFeAs and compare the outcome with similar measurements on as-grown and annealed BaFe2As2. In previous work on as-grown BaFe2As2, uniaxial pressure necessary to detwin the sample was found to induce a significant increase in zero pressure TN and Ts. However, we find that similar uniaxial pressure used to detwin NaFeAs and annealed BaFe2As2 has a very small effect on their TN and Ts. Since transport measurements on these samples still reveal resistivity anisotropy above TN and Ts, we conclude that such anisotropy cannot be due to uniaxial strain induced TN and Ts shifts, but must arise from intrinsic electronic anisotropy in these materials.

Magnetic interactions in iron superconductors: A review

“…In addition, the magnitude of the anisotropy is largest when the structural distortion and the magnetism are weaker [44][45][46][47][48]. Signatures of anisotropy have also been found in other experiments [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65]. The degeneracy of yz and zx is broken in both the magnetic and non magnetically ordered phases below the structural transition as revealed by ARPES [66][67][68] and X-ray experiments [69].…”

“…In addition, there is no agreement about the relevance of impurity scattering in the x/y resistivity anisotropy [48,53,58,[76][77][78][79]226]. Upon annealing, Ishida et al [76] find that the resistivity anisotropy of BaFe 2 As 2 nearly vanishes while significant anisotropy remains in Co-doped compounds.…”

“…The opposite resistivity anisotropy has been found in a holedoped material [63]. Anisotropy has also been measured in optical conductivity [59-62, 64, 223], elastic shear modulus [49,50], Raman [51], scanning tunnelling microscopy [52][53][54], magnetic torque [55] and inelastic neutron scattering experiments [56][57][58]65]. Signatures of orbital-dependent reconstruction of electronic structure in the magnetic and non-magnetic states are found in ARPES experiments [66-68, 224, 225] and in X-ray absortion spectroscopy [69].…”

“…A recent effective model sensitive to the orbital degree of freedom finds that spin fluctuations generate orbital splitting [75]. The possible role of impurities is also under investigation [48,53,58,[76][77][78][79]. Importantly, orbital or spin fluctuations are also likely candidates for the superconducting pairing glue: magnetic fluctuations are believed to mediate s +− -superconductivity [27,80], and orbital fluctuations are thought to lead to s ++ -superconductivity [74,81].…”

Evolution of antiferromagnetic susceptibility under uniaxial pressure in Ba(Fe1−xCox)2AsDhital1, Hogan2, Yamani3 et al. 2014Phys. Rev. B250150View full textAdd to dashboardCite

“…Numerous experimental probes such as dc transport [21,[28][29][30][31][32], optical conductivity [33][34][35][36], scanning tunneling microscopy [26,37], angle-resolved photoemission [10,12,13] neutron scattering [16,38,39], and magnetic torque measurements [25] have either directly or indirectly resolved the presence of the electronic behavior violating the C 4 rotational symmetry within the FeAs planes of different families of iron pnictide high-T c systems. Initial studies relied on bulk probes of crystals which manifested twin structural domains * stephen.wilson@bc.edu below their tetragonal-to-orthorhombic structural distortion temperatures (T S ).…”