Quantum spin dynamics

Abstract:

The FELIX free-electron laser is continuously tuneable over the wavelength range 5-100 mu m and can provide great power and the possibility of time-resolved experiments in the ns to mu s range. We describe a pulsed magnet specifically designed for semiconductor experiments using FELIX, which provides fields of up to 45 T, with a pulse-shape tailored to the macropulses of the FELIX source. The magnet consists of a conventional outer coil providing fields of up to 30 T with a pulse length of several ms, plus a single-layer inner coil with a rise-time of similar to 10 mu s, matched to duration of the FELIX macropulses. The magnet is to be extended to fields of up to 60 T. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We have performed the first cyclotron resonance studies of high mobility two-dimensional hole systems (2DHS) under pressure. Experiments were carried out using millimetre wave radiation on GaAs-(Ga, Al)As heterojunctions. Pressures were applied using a clamp cell specially designed for millimetre wave measurements. Our data at ambient pressure show collectively coupled resonances arising from interactions between the two hole systems with different effective masses formed by the spin-split halves of the lowest heavy-hole subband. The application of pressure appears to completely suppress the collective effect and only a resonance corresponding to the lighter cyclotron mass from the heavy-hole spin-split subband is observed. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

Measurements of the magnetic-field dependent millimetre-wave response of Cs2CuCl4, a quasi-one-dimensional Heisenberg antiferromagnet, are presented. The evolution of the electron spin resonance between high temperatures (the paramagnetic regime) and temperatures below T-N, at which there is an onset of long-range magnetic order (the antiferromagnetic regime), is studied for a range of crystal orientations. The magneto-optical data suggest that there is an onset of local magnetic order at temperatures considerably higher than T-N as determined from neutron scattering measurements, and that the evolution towards a long-range ordered state is gradual. A phenomenological model that describes the general features is suggested. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

A 60 T non-destructive pulsed magnet is developed for use with the continuously tuneable free electron laser "FELIX". Far infrared cyclotron resonance experiments were performed using the energy range of FELIX (5-100 mu m) to study the effect of strong confinement on the charge carriers in delta-doped InSb. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

The combination of a 60 T pulsed-field magnet and the continuous tunability of a high power, picosecond free-electron laser provides a powerful facility to study, e.g. cyclotron resonance in a wide range of materials with different effective masses and over a wide range of energies. Here we present the first cyclotron resonance data obtained with this new and unique combination of far-infrared radiation and high magnetic fields. (C) 1998 Elsevier Science B.V. All rights reserved.