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Experimental evidence is presented for the appearance of new plateaux in the differential conductance of a ballistic 1D channel in the high DC bias regime. In zero magnetic field, the authors observe steps in the differential conduction of e2/h, as opposed to the conventional value of 2e2/h for a spin-degenerate 1D subband. The new plateaux are found to be at quantised values to an accuracy of a few per cent and are described well by a model that assumes the bias is dropped symmetrically in the 1D channel. In addition, all the plateaux disappear with increasing DC voltage bias which can be explained in terms of an enhancement of the tunnelling probability. The same effects persist in a transverse magnetic field and the authors are able to calculate subband spacings as a function of the applied magnetic field.

Quantum oscillations of de Haas-van Alphen and Shubnikov-de Haas and semiclassical angular oscillations of the magnetoresistance have been observed in the quasi-two-dimensional organic metal α-(BETS)2TlHg(SeCN)4. The quantum oscillations are connected with the cylindrical part of the Fermi surface. The angular oscillations are associated with the carrier motion on both the cylindrical part and quasi-planar sheets of the Fermi surface. The values of the Dingle temperature, TD ≈ 2–3 K, and the effective mass, m* ≈ 1.03m0, have been defined. The possibility of the weakening of multibody interactions has been shown in this compound.

We study quantum (Shubnikov-de Haas and de Haas-van Alphen) oscillations and angular oscillations of the reluctance in the organic quasi-two-dimensional metal (BO)2Clx(H2O)y. We show that the Fermi surface in this compound consists of a slightly corrugated cylinder with its axis perpendicular to the conducting plane. The cross section of the cylinder in this plane is a perfect circle of radius k F≃3×107 cm−1. The effective carrier mass associated with this cylinder is m*=(1.65–2.0) m 0 in the conducting plane, while the Dingle temperature is T D=3–4 K.

We report angle-dependent magnetoresistance experiments on the charge-transfer salt ( alpha -ET2KHg(NCS)4 using fields of up to 30 T. The data indicate that the widely reported high-field 'kink' observed in the magnetoresistance of the alpha -ET2MHg(NCS)4 (M=K, Tl, Rb) family of charge-transfer salts represents a transition from an imperfectly nested spin-density wave ground state, characterized by a quasi-one-dimensional Fermi surface sheet tilted with respect to the b*c plane, to a state with a cylindrical two-dimensional Fermi surface.

Some of the recent measurements carried out on semiconductor nanostructures using the far-infrared and high magnetic field facilities of the High Field Magnet Laboratory of the University of Nijmegen are reviewed. In addition, a brief summary of high field studies of other semiconductor systems is given.

For pt.I see ibid., vol.23, p.1447 (1990). In theoretical studies of flocculation kinetics one usually assumes that the flocculation process reaches a steady state very rapidly. This assumption is invalid when a long-range attraction between the particles is present. In this paper the authors show that such a situation occurs for magnetic flocculation, provided that the particles are not too small. A full mathematical description of such a process is very difficult. As an alternative, a modified version of von Smoluchowski's model for rapid flocculation is presented, which describes the qualitative features of their experimental observations of aqueous Mn2O3 colloids with a particle diameter of about 0.8 mu m quite well. In particular this model suggests that the deviations from the 'steady-state' predictions increase very rapidly with increasing particle size, making these results almost always incorrect for many practical applications of magnetic flocculation.

The spin-doublet splitting and effective-mass shift of the cyclotron resonance in n -GaAs has been studied in high static magnetic fields applied along the (001), (011) and (111) crystal directions. A clear anisotropy of the conduction band has been observed in the orientation dependence of the spin-doublet splitting. The experimental results are described using a five-level k·p model. Comparison between the experimental data and this theoretical model allowed the determination of important band-structure parameters for GaAs, such as the interband momentum matrix element Q .

The transport properties of submicron channels in accumulation layer Si MOSFETs have been investigated in the quantum Hall regime. The channels are sufficiently narrow that ϱ xx takes non-zero values in the quantum Hall condition. We have found a series of Aharonov-Bohm oscillations in magnetoresistance in the regions of the i = 2 and i = 4 plateaux, with a reduction of a factor of 2 in the frequency at the higher filling factor. The amplitude of the oscillations can be very large, about 80%, and indicates discrete impurity scattering events between edge states. We have also found that the valley splitting in the Shubnikov-de Haas oscillations is not present in narrow channels.

Recent work on far-infrared and interband magneto-optical studies done at the High Field Magnet Laboratory of the University of Nijmegen will be reviewed.

The resonant coupling of the subband-Landau-levels in the two-dimensional electron gas (2DEG) of high mobility GaAs-AlGaAs heterojunctions has been studied using cyclotron resonance (CR). When the applied magnetic field has a component in the plane of the 2DEG, the electron motion parallel and perpendicular to the interface is coupled and the degeneracy of Landau levels belonging to different electric subbands will be lifted; this coupling will lead to hybridisation of the subband-Landau-levels. A splitting of the CR is observed when ℏωc coincides with the transition energy E 10 between the two lowest subbands [1]. This effect was observed some time ago by SCHLESINGER, HWANG and ALLEN [2].