Small-angle neutron scattering study of the vortex lattice in superconductingLuNi2B2C

Abstract

We present studies of the magnetic field distribution around the vortices in LuNi 2 B 2 C. Small-angle neutron scattering measurements of the vortex lattice ͑VL͒ in this material were extended to unprecedentedly large values of the scattering vector q, obtained both by using high magnetic fields to decrease the VL spacing and by using higher order reflections. A square VL, oriented with the nearest-neighbor direction along the crystalline ͓110͔ direction, was observed up to the highest measured field. The first-order VL form factor, ͉F͑q 10 ͉͒, was found to decrease exponentially with increasing magnetic field. Measurements of the higher-order form factors, ͉F͑q hk ͉͒, reveal a significant in-plane anisotropy and also allow for a real-space reconstruction of the VL field distribution.

Atomic resolution and vortex lattice studies of magnetic superconductors: A first approach in the nickel borocarbide TmNi2B2C

“…However, changes in the vortex lattice symmetry can appear when coupling with the electronic and magnetic structure becomes relevant. For instance, a hexagonal to square transition has been observed using STM in the non-magnetic nickel borocarbides when Bkc around 0.15 T. At high enough vortex densities, the four-fold anisotropy of the Fermi surface at the basal plane of the crystal structure, leads to anisotropic effects on the vortex interactions and to a square vortex lattice [49,50,25,51,21]. The results seen here in TmNi 2 B 2 C, when Bkc (Fig.…”

Vortex lattices in type-II superconductors studied by small-angle neutron scattering

“…A more thorough justification of this choice is given in Ref. [6]. Note that F (q 00 ) is simply the applied magnetic field μ 0 H. Figure 9(a) shows the field reconstruction obtained using Eq.…”

Field dependence of the superconducting basal plane anisotropy of TmNi2B2C

“…Nonetheless, Table I shows that increasing the field from 0.2 to 0. As shown by Densmore et al, 16 a conceptually simple and model-independent method to obtain a measure of the basal plane anisotropy is by a real space magnetic field reconstruction using…”

“…Table I, one finds a substantial difference, unlike our earlier measurements on LuNi 2 B 2 C where the two were found to be in excellent agreement. 16 A theoretical analysis of the interdependence of the superconducting and magnetic properties of TmNi 2 B 2 C by Jensen and Hedegård gives an estimate of the orbital critical field H c2,orb = 4.3 T at 1.6 K, 23 yielding a zero-field coherence length of 8.75 nm. However, this ignores the contribution to the core size from the spin-polarized quasi-particles in the vortex core and we thus expect that ξ J obtained from the field reconstruction to be a more accurate measure of the actual vortex core size.…”

“…This is possible by measuring a large number of higher order VL reflections in a manner analogous to our previous study of non-magnetic LuNi 2 B 2 C (no Pauli paramagnetic effects and no reentrance of the square VL phase). 16 Our measurements allow a quantitative determination of the four-fold basal plane anisotropy and show a monotonic decrease with increasing field.…”