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.

The present paper describes unique experimental techniques developed for minimizing disturbances due to transient electromagnetic fields during a capacitor discharge into a small single turn coil, generating magnetic fields above the megagauss limit. Results of cyclotron resonance measurements are presented as example of the capability of the experimental set-up to resolve transmission changes being smaller than one percent.

The Faraday effect is measured in paramagnetic terbium gallate garnet Tb3Ga5O12 at a wavelength λ=0.63 µm at 6 K in pulsed magnetic fields up to 75 T increasing at a rate of 107 T/s for field orientation along the crystallographic direction 〈110〉. The experimental data are compared with the results of theoretical calculations taking into account the crystal fields acting on the Tb3+ ion and various contributions to the Faraday rotation. Since the measurements in pulsed fields are carried out in the adiabatic regime, the dependence of the sample temperature on the magnetic field acting during a current pulse is obtained from the comparison of the experimental dependence of Faraday rotation with the theoretically calculated dependences of the Faraday effect under isothermal conditions at various temperatures.

The differential magnetic susceptibility of intermetallic compounds RMn2Ge2 (R=Gd, Tb, Dy, Ho, Y) with a layered tetragonal structure is measured in pulsed magnetic fields up to 130 T. It is found that all these compounds undergo a first-order magnetic phase transition in strong magnetic fields. The nature of this transition is discussed, and it is found that a change in the magnetic state of the manganese sublattice is responsible for the transition.

We report on infrared magneto-transmission experiments in the multi-megagauss range up to 700T on p-type epitaxially grown cubic GaN-samples. The experiments up to 700 T using the explosive flux-compression are in excellent agreement with the results obtained by the single-turn coil technique up to 270T.

We demonstrate for HgSe epitaxial layers that transient magnetic fields in the megagauss regime prove as a new tool to investigate detailed information on spin-lattice relaxation using the delayed population change of the spin levels in the presence of rapidly varying magnetic fields up to 150 T.

The “Humboldt High Magnetic Field Center” is operated by the chair for “Magnetotransport in Solids” at the Institute of Physics of the Humboldt University at Berlin. Three different kinds of magnetic field generators cover the range up to 300T. All field generators are intended for operation in temperatures ranging between 0.3K and room temperature. Magnetization measurements use both Faraday rotation and compensated pick-up coils. To probe spin and charge carrier systems electromagnetic radiation sources from the visible part of the spectrum to mm-waves are available. Special emphasis is laid on sophisticated measuring- and data acquisition techniques enabling us to obtain a sensitivity in transmission experiments in megagauss fields that is usually achieved only in DC-fields applying multi-sampling methods. The installations of the “Humboldt High Magnetic Field Center” are open to all interested scientists on a mutual cooperation basis.

We report on the first successful cyclotron resonance experiment on a semiconductor in ultrahigh magnetic fields generated by explosive-driven flux compression. The sample under investigation was a p-type cubic GaN layer grown by plasma-assisted MBE on a (001)-GaAs substrate. We have used the magnetocumulative generator MC-1 for generating a magnetic field exceeding 700T. A CO2 laser with a fixed wavelength of λ=10.6μm was used as radiation source. The transmitted radiation intensity was detected by use of a fast HgCdTe-detector. The experiment was performed at 270K in Faraday geometry with the magnetic field oriented parallel to the [001]-direction of the epitaxial layer. Three distinct transmission minima at about 90T, 270T and 400–425T with a resonance depth of a few percent only, are clearly resolved. The data in the lower field region correspond excellently to results derived previously from experiments in fields up to 275T generated by use of the single-turn coil technique. The data are compared directly with the Landau level scheme of cubic GaN in the Luttinger model.

We report on the first successful IR-cyclotron resonance experiment in ultrahigh magnetic fields up to 700 T generated by explosive driven flux compression. The sample under investigation was an epitaxially grown p-type cubic GaN-layer. Three distinct transmission minima, due to inter-valenceband transitions at about 90 T, 270 T and 400 T - 430 T with a resonance depth of a few percent only, are clearly resolved. The data in the lower field region correspond excellently to results derived previously from experiments in fields up to 275 T generated by use of the single-turn coil technique.

Transient magnetic fields in the megagauss regime prove as a new tool to investigate detailed information on spin-lattice relaxation using the delayed population change of the spin levels in the presence of rapidly varying magnetic fields. The method is applied to HgSe and HgTe epitaxial layers in magnetic fields up to 150T.

High-field magnetization measurements using the single-turn coil technique not only give detailed information on the critical magnetic field of level crossing anomalies in the rare-earth zircons TmPO4 and PrVO4, but also provide strong evidence of hysteresis effects in up- and down-sweep of the external magnetic field.

Magnetic anomalies caused by an energy level interaction in a high magnetic field are investigated experimentally and theoretically for a Van Vleck paramagnet PrVO4. Maxima of the differential susceptibility dM/dH associated with a crossing of the lowest-lying levels at the field HC≈51.3T are observed for various temperatures. The hysteresis is detected, which is ascribed to the relaxation processes. The magnetocaloric effect calculated on the assumption of adiabatic magnetization at pulsed fields shows the monotonous decrease of the temperature with increasing field up to HC and its subsequent increase. The problem of spin-lattice relaxation times in the vicinity of crossover is discussed. The great importance of the hyperfine coupling in the crossover effects for the PrVO4, which is among the enhanced nuclear magnets, is emphasized.

IR-megagauss spectroscopy on HgSe provides information on both intra- and inter-band transitions resulting in a new set of k*p-parameters for high magnetic field application. Transient effects in the resonance intensities are due to hysteresis effects in the spin dependent population and provide a novel tool for the determination of the spin-lattice relaxation.

A Data of the electron cyclotron resonance at the L-point in GaAs are presented in comparison with theoretical predictions of P. Vogl and coworkers. The experiment was performed in multi-megagauss magnetic fields up to 1000 T within the framework of the KAPITZA series of experimental seminars using explosive flux-compression at a temperature of T = 280 K. As sample we have used (110) oriented bulk material with an electron concentration of about n = 2*10(18) cm(-3). The 10.6 mum wavelength radiation was transmitted through the sample in Faraday configuration. Possible mechanism pf the population of the states at the L-point are discussed in detail.

We report on magnteospectroscopical investigations on HgSe in the infrared wavelength range using very high pulsed magnetic fields. We have observed interband transitions as well as the cyclotron resonance (CR) of quasi free electrons. Transient effects in the resonance intensities are due to hysteresis effects in the spin dependent population and provide a novel tool for the determination of the spin-lattice relaxation time.

We report on the first successful IR-cyclotron resonance experiment in ultrahigh magnetic fields up to 700 T generated by explosive driven flux compression. The sample under investigation was an epitaxially grown p-type cubic GaN-layer, a material which has become worldwide the subject of extensive experimental and theoretical investigations because of its application in optoelectronic devices operating in the blue-to-violet wavelength range. Three distinct transmission minima at about 90 T, 270 T and 400 T-430 T with a resonance depth of a few percent only, are clearly resolved. The data in the lower field region correspond excellently to results derived previously from experiments in fields up to 275 T generated by use of the single-turn coil technique.

Magnetotransmission studies of EuS/PbS multiquantum wells in magnetic fields up to 200 T and in the temperature range from 5 to 300 K are reported. A series of transitions are observed, which we interpret as cyclotron resonance transitions, i.e., the transitions between the lowest magnetic subbands. With this identification, the positions of observed resonances are satisfactorily described by theory when the quantum well width is larger than 100 Angstrom. For narrower quantum wells, however, the discrepancy between theory and experimental measurements is significant. Possible explanations for this discrepancy are discussed.

We report on the design and performance of a megagauss generator at the Humboldt High Magnetic Field Centre. The installation uses the fast capacitor discharge into single-turn coils to produce microsecond pulses of 260 T in 8 mm diameter suitable for low-temperature experiments and 310 T in 5 mm diameter. Simple concepts are applied to substantiate crucial design principles for the generator and the choice of components. The implementation of a high-power/low-inductance circuit operated at 60 kV and other technical questions are discussed in detail. The analysis of experimental field and current data is based on numerical simulations of the magnetic pressure and the nonlinear flux diffusion. It was carried out in order to investigate the limitations and characteristics of the Berlin generator in particular and the single-turn coil technique in general. The paper focuses primarily on field, generator and coil parameters, which can be used for performing routine, reproducible scientific experiments at low temperatures.