Frustrated interactions exist throughout nature, with examples ranging from protein folding through to frustrated magnetic interactions. Whilst magnetic frustration is observed in numerous electrically insulating systems, in metals it is a rare phenomenon. The interplay of itinerant conduction electrons mediating interactions between localised magnetic moments with strong spin-orbit coupling is likely fundamental to these systems. Therefore, knowledge of the precise shape and topology of the Fermi surface is important in any explanation of the magnetic behaviour. PdCrO2, a frustrated metallic magnet, offers the opportunity to examine the relationship between magnetic frustration, short-range magnetic order and Fermi surface topology. By mapping the short-range order in reciprocal space and experimentally determining the electronic structure, we have identified the dual role played by the Cr electrons in which the itinerant ones on the nested paramagnetic Fermi surface mediate the frustrated magnetic interactions between local moments.

A method for computing electron momentum densities and Compton profiles from ab initio calculations is presented. Reciprocal space is divided into optimally-shaped tetrahedra for interpolation, and the linear tetrahedron method is used to obtain the momentum density and its projections such as Compton profiles. Results are presented and evaluated against experimental data for Be, Cu, Ni, Fe3Pt, and YBa2Cu4O8, demonstrating the accuracy of our method in a wide variety of crystal structures.

Hugenschmidt, C. (2015). Spin-resolved fermi surface of the localized ferromagnetic Heusler compound Cu2MnAl measured with spin-polarized positron annihilation. Physical Review Letters, 115(20) We determined the bulk electronic structure of the prototypical Heusler compound Cu 2 MnAl by measuring the angular correlation of annihilation radiation using spin-polarized positrons. To this end, a new algorithm for reconstructing 3D densities from projections is introduced that allows us to corroborate the excellent agreement between our electronic structure calculations and the experimental data. The contribution of each individual Fermi surface sheet to the magnetization was identified, and summed to a total spin magnetic moment of 3.6 AE 0.5 μ B =f:u:.

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First-principles calculations of the electronic structure and phonon dispersion relation of the superconducting compound BaSn5 were performed. This has allowed the calculation of the electronphonon matrix elements from which the electron-phonon coupling constant was found to be λep = 0.87. Application of the Allen-Dynes formula with µ * = 0.11 yielded a superconducting transition temperature of Tc = 4.2 K. The calculated Tc agrees well with the available experimental data and indicates that BaSn5 is an electron-phonon superconductor with intermediate strength electronphonon coupling.