A hysteresis loop is observed for the first time in the de Haas-van Alphen (dHvA) effect of beryllium at low temperatures and quantizing magnetic field applied parallel to the hexagonal axis of the single crystal. The irreversible behavior of the magnetization occurs at the paramagnetic part of the dHvA period in conditions of Condon domain formation arising by strong enough dHvA amplitude. The resulting extremely nonlinear response to a very small modulation field offers the possibility to find in a simple way the Condon domain phase diagram. From a harmonic analysis, the shape and size of the hysteresis loop is constructed.

Below a critical filling factor (v c =0.2&) and critical temperature (Tc^XA K at 26 T) an additional line has been observed in the luminescence spectrum of a GaAs-Al x Gaix As heterojunction; it grows in intensity with decreasing v, dominating the spectrum at v < 17 • Its appearance is accompanied by a strong reduction in overall integrated intensity, while its relative intensity decreases sharply at v = K j, and f. The lack of correlation between v c and the disorder-related properties of the system indicates the intrinsic nature of the line which we propose signals the formation of a pinned Wigner solid.

We report measurements of the de Haas-van Alphen (dHvA) effect in the quasi-two-dimensional organic metal κ-(BEDT-TTF)2Cu(NCS)2 by means of a capacitive torquemeter. The experiments were carried out in magnetic fields up to 29.5 T, at temperatures down to 0.4 K and for tilt angles θ between -35° and 80°. In the angular dependence of the fundamental frequency we observed five spin-zeros, the absolute amplitude at θ = 0° amounts to μ0M = 4·10-6 T (B = 13.8 T, T = 1.4 K). Above 15 T a series of high-frequency oscillations due to magnetic breakdown is observed. The main breakdown orbit could be detected up to θ = 55°, the angular dependence is also characterized by spin-splitting effects. We determined the effective cyclotron mass of three different breakdown orbits at θ = 5.6°. Our results are in good agreement with a simple model of magnetic breakdown. The occurrence of weak oscillations forbidden within this model is discussed.