N. Puhlmann

Energy level crossing effects in the rare-earth zircons TmPO4 and PrVO4

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.

The Megagauss facility of the HUMBOLDT high magnetic field center in Berlin

Abstract We report on concept. realisation, and first experimental results obtained with the preliminary megagauss equipment of the HUMBOLDT High Magnetic Field Center. The present megagauss set-up is a handy, transportable single-turn coil equipment using only 20% of the capacity of the final installation, i.e. 50 kJ at 60 kV producing about 100 and 200 T in the single-turn coils of 10 and 5 mm diameter, respectively. Test reports on magnetooptical measurements at low temperature are presented.

Peculiarities of energy level crossing effects in a singlet paramagnet PrVO4

Abstract Magnetic anomalies caused by an energy level interaction in a high magnetic field are investigated experimentally and theoretically for a Van Vleck paramagnet PrVO 4 . Maxima of the differential susceptibility d M /d H associated with a crossing of the lowest-lying levels at the field H C ≈51.3 T 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 H C 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 PrVO 4 , which is among the enhanced nuclear magnets, is emphasized.

Intra- and inter-band transitions in HgSe in megagauss fields

Abstract 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.

Spin dynamics in megagauss fields

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 150 T.

Investigation of HgSe/HgSe:Fe quantum wells and super lattices

High-field magnetospectroscopy measurements on HgSe/HgSe :Fe quantum wells and superlattices are reported. Fe 2+ substitution of Hg 2+ manifests itself in a donor about 210 meV above the conduction band edge and thus for sufficiently high carrier concentration as a Fermi level pinned system in the mixed valence regime. The MBE-grown samples on ZnTe/GaAs substrates exhibit 2D effects for characteristic well or superlattice dimensions < 20 nm. Strong anisotropy effects due to strain are observed. By variation of the size quantization the predicted transition from a 2D to 3D QHE for Fermi level pinned systems is demonstrated.

HIGH SENSITIVITY MEGAGAUSS SPECTROSCOPY

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.

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.

Semiconductor magneto-spectroscopy in semidestructive and destructive magnetic fields up to 700 T

We report on infrared magneto-transmission experiments in the multi-megagauss range up to 700 T 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 270 T.

IR cyclotron resonance of solid states in magnetic fields up to 700 tesla

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.