Electrical resistivity and magnetic susceptibility studies of the system Mn5Si3-Fe5Si3

Electrical resistivity measurements have been performed on the system Mn_5?x,Fe_xSi₃ for the compounds x = 0,1,2,3,4 and 5 from 4.2 K to above room temperature. From the shape of the ρ(T) curves it can be inferred that the transition from antiferromagnetic to ferromagnetic ordering occurs in the concentration range 3 ? x ? 4; for Fe₅Si₃ and MnFe₄Si₃ the ρ(T) curves are characterized by a break in their slope, whereas for x = 1,2 and 3 a large minimum appears. Mn₅Si₃ exhibits two successive minima at 74 and 105 K. Magnetic susceptibility measurements for x = 1, 2 and 3 give confirmation of the Néel temperature for x = 1 and 2, whereas for x = 3 the behaviour is more complex.     

Coherent ultra-short pulse semiconductor spectroscopy and non-Lorentzian line shapes

It is shown that the experimental observation of the excitonic optical Stark effect with relatively long pulses can only be understood if a frequency-dependent exciton damping is taken into account, which decreases rapidly with increasing detuning.     

Phonon-assisted Auger recombination in Si with direct calculation of the overlap integrals

The overlap integrals are calculated for Si by means of the full zone double group k · p-method whereas they are usually roughly estimated. The results confirm that phonon-assisted Auger recombination is the predominating radiationless recombination mechanism in indirect band gap semiconductors. This holds not only for highly doped materials but also for electron- hole drops.     

On the gain spectrum of highly excited GaAs

We compare the results of our theory of the dielectric function for an electron—hole plasma with a series of experimental gain spectra for GaAs, which have been obtained by tuning the frequency of the exciting laser.