Interaction between spin, lattice, and charge in non-centro\-symmetric correlated metals

• Applicant: Professor Dr. Rudolf Hackl
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 269710404

This renewal proposes light scattering experiments on carefully selected non-centrosymmetric materials to clarify carrier dynamics in the presence of complex magnetic order. This will complete and extend the work on MnSi that was successfully performed during the first funding period after implementing several crucial technical innovations. In MnSi the phonons were shown to provide relevant information on the transition into the magnetically ordered phase and the fluctuation-dominated range above the Curie temperature. Symmetry-dependent electron dynamics were associated with different sheets of the Fermi surface. In the magnetically ordered state the relaxation rates found in the Raman experiments exhibited a temperature dependence significantly different from that expected from transport. We speculate that the the electrons scatter from complex spin textures such as helices or skyrmions; yet, as opposed to longitudinal or transverse transport, this has no theoretical foundation. It is one of the objectives of the renewal to clarify questions about the role of exotic excitations in materials with complex spin order such as MnSi. To this end we plan experiments on MnSi with applied hydrostatic pressure and field. With the equipment at hand we are optimally prepared to access the quantum disordered phase above 1.46GPa. Here the resistivity varies as T^{3/2}, a significant deviation from the T^2 Fermi liquid-like behavior observed in the helimagnetic phase. With an applied pressure of approximately 1 GPa the skyrmion or A-phase has the largest extension in the phase diagram and the strongest impact on the topological Hall effect. In the Raman spectra we thus expect to observe signatures enabling us to derive related momentum dependent carrier properties. We intend to study the interrelation between these fundamental basic properties and putative functionalities via experiments on Mn0.92Fe0.08Si and Mn0.96Co0.04Si. Finally, it is envisaged to extend the work from d- to f-electron systems such as CePt3Si, CeIrSi3, and CeTAl3 (T=Cu, Ag, Au, Pd, Pt) having ferromagnetic, antiferromagnetic, and superconducting phases in close proximity. In all material classes the respective phase diagrams will be accessible with the unique equipment assembled during the first funding period. In close collaboration with our partners we plan in-depth studies of the elementary excitations using complementary experimental methods. Simultaneous theoretical analysis is intended to identify the interactions which are most relevant for the carrier dynamics.

• DFG Programme: Research Grants
• Cooperation Partner: Professor Dr. Rudolf Gross