Biomedical subjects

Ch Niedermayer

Publications and source records attributed to Ch Niedermayer.

3 recordsLinked to original sources

PubMed2005

Quantum statistics of interacting dimer spin systems.

The compound TlCuCl(3) represents a model system of dimerized quantum spins with strong interdimer interactions. We investigate the triplet dispersion as a function of temperature by inelastic neutron scattering experiments on single crystals. By comparison with a number of theoretical approaches we demonstrate that the description of Troyer, Tsunetsugu, and Würtz [Phys. Rev. B 50, 13 515 (1994)10.1103/Phys. Rev. B 50, 13515] provides an appropriate quantum statistical model for dimer spin systems at finite temperatures, where many-body correlations become particularly important.

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PubMed2004

Effect of two gaps on the flux-lattice internal field distribution: evidence of two length scales in Mg(1-x)AlxB2 from muSR.

We have measured the transverse field muon spin precession in the flux-lattice (FL) state of the two-gap superconductor MgB2 and of the electron doped compounds Mg(1-x)AlxB2 in magnetic fields up to 2.8 T. We show the effect of the two gaps on the internal field distribution in the FL, from which we determine two coherence length parameters and the doping dependence of the London penetration depth. This is an independent determination of the complex vortex structure already suggested by the STM observation of large vortices in a MgB2 single crystal. Our data agree quantitatively with STM and we thus validate a new phenomenological model for the internal fields.

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PubMed2003

Observation of the conduction electron spin polarization in the Ag spacer of a Fe/Fg/Fe trilayer.

The spatially oscillating electron spin polarization in the Ag spacer of a 4 nm Fe/20 nmAg/4 nm Fe(001) epitaxial trilayer has been determined by means of low energy muon spin rotation. It oscillates with the same period as the interlayer exchange coupling, but shows a much weaker attenuation at large distances x from the interface. The measured magnetization profile from the inner 14 nm of the spacer is described by an oscillating polarization decaying as x(-0.8(1)). This unusual behavior may arise from a full confinement of electron states within the spacer.

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