S. Hansel

Alignment Dynamics of Single-Walled Carbon Nanotubes in Pulsed Ultrahigh Magnetic Fields

We have measured the dynamic alignment properties of single-walled carbon nanotube (SWNT) suspensions in pulsed high magnetic fields through linear dichroism spectroscopy. Millisecond-duration pulsed high magnetic fields up to 56 T as well as microsecond-duration pulsed ultrahigh magnetic fields up to 166 T were used. Because of their anisotropic magnetic properties, SWNTs align in an applied magnetic field, and because of their anisotropic optical properties, aligned SWNTs show linear dichroism. The characteristics of their overall alignment depend on several factors, including the viscosity and temperature of the suspending solvent, the degree of anisotropy of nanotube magnetic susceptibilities, the nanotube length distribution, the degree of nanotube bundling, and the strength and duration of the applied magnetic field. To explain our data, we have developed a theoretical model based on the Smoluchowski equation for rigid rods that accurately reproduces the salient features of the experimental data.

Spin-glass behaviour and dynamical process of high field magnetisation in disordered perovskite manganites

In single crystals of A-site disordered perovskite manganites R1−xAExMnO3 (R = Sm, Gd, Eu, AE = Ba, Sr, x = 0.5, 0.45), we have observed the spin-glass behaviour. Applying pulsed high magnetic fields, a metamagnetic phase transition was observed in some samples, whereas in other samples, the magnetisation was just a smoothly varying function of magnetic field up to the saturation. The difference between the two types of behaviour seems to arise from the difference in the average ionic radius of the A-site ions and the disorder in the A-site layers. In the metamagnetic transition, magnetisation hysteresis was found to be smaller as the field sweep rate is faster, which is contrary to the ordinary spin relaxation phenomena.

Transient Megagauss Fields on Indium Antimonide and Mercury Cadmium Telluride

We present a careful analysis of previously reported data obtained in cyclotron resonance measurements in InSb using CO2 radiation and transient magnetic fields in the range of ≈ 50T. With the consideration of eddy currents incorporating Drude model like conductivity tensor we developed a quantitative determination of conductivity in transient fields. Using these values an explanation is found for data previously not understood. According to our considerations many other hysteretic phenomena can be qualitatively represented.

High-field magneto-spectroscopy in HgSe and HgTe up to 225 Tesla

We report on high-field magneto-spectroscopy in HgSe and HgTe using 10.6 /spl mu/m and 5.4 /spl mu/m wavelength radiation in magnetic fields up to 225 T using the single-turn-coil generator. The experimental data agree excellently with the theoretical prediction of suitable energy-band models.

Magnetotransport in HgSe:Fe quantum‐dots

We report on magnetotransport measurements in intrinsically populated HgSe:Fe quantum‐dot systems in magnetic fields up to 12 T. Depending on the dot density we observe positive and negative differential magnetoresistance, the later similar to hopping conductivity in impurity bands.

HgSe and HgSe:Fe in extreme magnetic fields

We present a tight binding approach to model energy levels of HgSe in high magnetic field. In this model we are able to explain all given experimental findings in low field and high field as well as in strained samples of lower dimension.

MAGNETOOPTICAL EXPERIMENTS USING THE EXPLOSIVE DRIVEN FLUX COMPRESSION UP TO 1000T

We discuss three recent magnetooptical experiments using the explosive driven flux-compression technique that have been performed in cooperation of the Berlinian with the Russian group of VNIIEF, Sarov. We present an overview on the experimental techniques touching the frontiers of physics as well as a detailed discussion of the results obtained on the semiconducting materials GaN, GaAs and HgSe. Special emphasis will be laid on the interpretation in context with theoretical predictions and analysis that go beyond the ordinary k•p-formalism but are also valid in the limit of the HOFSTADTER butterfly.