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Static and Elastic Properties of Superconducting Vortex Lattices and Skyrmion Lattices in Chiral Magnets Studied by Time Resolved Neutron Scattering

Sebastian Mühlbauer (Forschungsneutronenquelle Heinz Maier-Leibnitz, Germany)

Both superconducting vortex (VL) [1,2] and skyrmion lattices (SKL) in chiral magnets [3] can be regarded as macroscopic lattices, formed by topological entities. Analogous to condensed matter, a large variety of phases is also observed for vortex-matter (VM) and Skyrmion matter, resembling the particle like character and reflecting the underlying physical properties. Moreover, both VL and SKL represent ideal model systems for questions of general importance as topological stability and decay.

The elastic matrix Φαβ of a VL describes the energy of a distorted VL. We report direct measurements of the VL tilt modulus c44 in ultra-pure bulk Niobium using time-resolved stroboscopic SANS [2]. With its low GL parameter . situated at the border of type-I superconductivity, Niobium is ideally suited as a model system for studies of VM. By a periodic tilting of the magnetic field, we induce a relaxation process of the VL which shows increasing stiffness with increasing magnetic field and reduced damping with increasing temperature and agrees well with calculations performed within a diffusion model.

Skyrmion lines can be seen as magnetic whirls - sharing strong similarities with vortices of type II superconductors where the particle-like character of the Skyrmions is reflected in the integer winding number of their magnetization [3]. As for superconducting VM, SKL melting transitions, Skyrmion liquids and Skyrmion glass phases are expected to exist in the various B20 materials. Due to their topology, SKLs provide an excellent showcase for the investigation of topological phase conversion [4]. A further consequence of the special topological properties of Skyrmions is called emergent electrodynamics: While moving through the SKL, conduction electrons collect a Berry's phase in real space which leads to a very efficient coupling of transport current and magnetic structure. This leads to considerable spin transfer torque effects at current densities as low as 106 A/m2 [5].

Similar to our study on VLs, we present recent time-resolved SANS experiments on the elasticity of the SKL in MnSi, exploiting the technique TISANE. Our study paves the way how to access directly VL and SKL melting as well as their current induced motion and dynamic properties in bulk samples. Finally, we present the planned implementation of TISANE at the new SANS-1 instrument at FRM II, Munich.

*Work in collaboration with: J. Kindervater, T. Adams, A. Chacon, F. Jonietz, A. Bauer, A. Neubauer, W. Wünzer, R. Georgii, M. Janoschek, S. Dunsiger, P. Böni, C. Pfleiderer, M. Garst, K. Everschor-Sitte, C. Schütte, J. Waizner, S. Buhrandt, A. Rosch, P.Milde, L. Eng, J. Seidel, H. Berger, E. M. Forgan, M. Laver, E. H. Brandt, U. Keiderling, A. Wiedenmann

[1] S. Mühlbauer et al., Phys. Rev. Lett 102 136408 (2009)
[2] S. Mühlbauer et al., Phys. Rev. B 83, 184502 (2011)
[3] S. Mühlbauer et al., Science 323 915 (2009)
[4] P. Milde et al., Science 340, 6136, (2013)
[5] F. Jonietz et al., Science 330, 6011, 1648 (2010)

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