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.