Quantum spin dynamics

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.

Abstract:

We experimentally demonstrate a mechanism for a new kind of magnetic resonance, the Fermi-surface traversal resonance (FTR). This is caused by the periodic traversal of carriers across quasi-one-dimensional (Q1D) sections of Fermi surface (FS) in an external magnetic field. Owing to the warping of the Q1D Fermi sheets, the real space velocities of the carriers oscillate as they cross the FS, generating resonances in the high frequency conductivity of the material. The results contain information about the FS, including the direction and harmonic content of the warping components. Using a rotating resonant-cavity system, FTRs have been observed in α-(BEDT-TTF)2 KHg(SCN)4. © 1998 The American Physical Society.