Probing the anisotropic vortex lattice in the Fe-based superconductor KFe2As2using small-angle neutron scattering

Abstract

Using small angle neutron scattering, the anisotropy of the magnetic vortex lattice (VL), in the heavily hole-doped pnictide superconductor KFe 2 As 2 , was studied. Well-ordered VL scattering patterns were measured with fields applied in directions between B c and the basal plane, rotating either towards [100] or [110]. Slightly distorted hexagonal patterns were observed when B c. However, the scattering pattern distorted more strongly as the field was rotated away from the c axis. At low field, the arrangement of vortices is affected by the anisotropy of penetration depth in the plane perpendicular to the field. By fitting the distortion with the anisotropic London model, we obtain an estimate of ∼3.4 for the anisotropy factor γ between the in-plane and c-axis penetration depths at the lowest temperature studied. The results further reveal VL phase transitions as a function of field direction. We discuss these transitions using the "hairy ball" theorem.

Doping evolution of the second magnetization peak and magnetic relaxation in (Ba1−xKx)FLiu1, Zhou2, Sun3 et al. 2018Phys. Rev. B13170View full textAdd to dashboardCite

“…15, we show the effect of cooling rate on the dip for the sample x=0. 32. With applying the fast cooling rate at 10 K/min and slow cooling rate at 1 K/min, the dip shifts ~0.2 K toward the low temperature 21 regime.…”

“…In optimally doped BaFe 2 (As 0.67 P 0.33 ) 2 single crystals, hexagonal VL was formed in the field range from 1 to 16 T revealed by SANS measurement, and no symmetry changes in the VL were observed [30]. In KFe 2 As 2 single crystals, a well-ordered hexagonal VL was observed by SANS measurement, with no symmetry transitions up to high fields [31][32].…”

Magnetic small-angle neutron scattering

“…For fields parallel to the basal plane Γ VL = Γ ac . Here, Γ ac mainly reflects the anisotropy of the Fermi velocity in the ac plane, and in general one expects Γ ac = λ c /λ ab (Kawano-Furukawa et al, 2013). Even in cases where measurements with an exact in-plane field are not possible, Γ ac can be obtained by extrapolation.…”

Simultaneous evidence for Pauli paramagnetic effects and multiband superconductivity inKFe2As2by small-angle neutron scattering studies of the vortex lattice

“…For more than half a century small-angle neutron scattering (SANS) has been used to study the vortex lattice (VL) in a wide range of materials, [17][18][19][20][21][22] and has provided often unique information about gap nodes and dispersion, 6,[23][24][25] non-local effects, 26,27 multiband superconductivity, 28 Pauli paramagnetic effects, [29][30][31][32] and a direct measure of the intrinsic superconducting anisotropy (Γ ac ). [32][33][34][35][36][37][38] The latter quantity may be directly measured by the field-angledependent distortion of the VL structure (Γ VL ) from a regular hexagonal pattern. In London theory Γ ac represents the anisotropy of the penetration depth.…”