arXiv subjects

F. Demmel

Publications and source records attributed to F. Demmel.

20 records · Page 2Linked to original sources

arXiv2005

Spin-wave dispersion in orbitally ordered La(0.5)Sr(1.5)MnO(4)

The magnon dispersion in the charge, orbital and spin ordered phase in La(0.5)Sr(1.5)MnO(4) has been studied by means of inelastic neutron scattering. We find an excellent agreement with a magnetic interaction model basing on the CE-type superstructure. The magnetic excitations are dominated by ferromagnetic exchange parameters revealing a nearly-one dimensional character at high energies. The nearest neighbor ferromagnetic interaction in La(0.5)Sr(1.5)MnO(4) is significantly larger than the one in the metallic ferromagnetically ordered manganites. The large ferromagnetic interaction in the charge/orbital ordered phase appears to be essential for the capability of manganites to switch between metallic and insulating phases.

cond-mat.str-el↗

arXiv2004

Collective Dynamics of Lipid Membranes studied by Inelastic Neutron Scattering

We have studied the collective short wavelength dynamics in deuterated DMPC bilayers by inelastic neutron scattering. The corresponding dispersion relation $\hbarω$(Q) is presented for the gel and fluid phase of this model system. The temperature dependence of the inelastic excitations indicates a phase coexistence between the two phases over a broad range and leads to a different assignment of excitations than that reported in a preceding inelastic x-ray scattering study [Phys. Rev. Lett. {\bf 86}, 740 (2001)]. As a consequence, we find that the minimum in the dispersion relation is actually deeper in the gel than in the fluid phase. Finally, we can clearly identify an additional non-dispersive (optical) mode predicted by Molecular Dynamics (MD) simulations [Phys. Rev. Lett. {\bf 87}, 238101 (2001)].

cond-mat.soft↗