Y. Imanaka

Low-dimensional systems in ultra-high magnetic fields: magnetic-field-induced type I to type II transitions in short-period semiconductor superlattices

We present a review on the recent study of the type I to type II transition in short-period superlattices of GaAs/AlAs by means of cyclotron resonance and interband magneto-optical spectroscopy in pulsed high magnetic fields up to 500 T. In the magneto-photoluminescence spectra of excitons in , the magnetic-field-induced type I to type II transition was observed with and without the simultaneous application of high pressure. The behaviour of the transition varies depending on the thickness of the AlAs layers. In cyclotron resonance of , the resonance peak at the X minima was observed in the type II regime for n smaller than 14, whereas the resonance at the point was observed for n>15. It was found that the angular dependence of the peak position does not obey the simple cosine dependence due to the subband mixing in high magnetic fields. From the angular dependence, the effective masses at the X point were determined. In high-field cyclotron resonance measurements at 129 meV up to 400 T for n = 16 (type I), the resonance of the X minima expected at around 260 T was indiscernible, despite the fact that the transition should have occurred at lower fields.

Angular dependent cyclotron resonance in short period (GaAs)n/(AlAs)n superlattices

Abstract Cyclotron resonance (CR) measurements have been carried out to evaluate the effective masses of electrons at the AlAsX point of the Brillouin zone in short period (GaAs)n/(AlAs)n superlattices (SLs) with n = 8–14. The longitudinal effective mass was deduced to be m1 = 1.04m0 by analyzing a deviation of CR position from the cos φ-dependence for tilted magnetic fields in (GaAs)14/(AlAs)14 SL.

Collective cyclotron modes in high-mobility two-dimensional hole systems in GaAs - (Ga, Al)As heterojunctions: II. Experiments at magnetic fields of up to forty Tesla

The cyclotron resonance of very high-mobility holes in GaAs - (Ga, Al)As heterojunctions grown on (111), (311) and (100) substrates has been studied in high magnetic fields of up to 40 T. As the temperature is increased from to , the cyclotron resonance is found to shift to lower magnetic fields, the size of shift depending on the cyclotron frequency and the substrate orientation. These observations may be explained using the model of interacting hole subsystems developed by Cole et al.

Cyclotron resonance in short period (GaAs)n/(AlAs)n superlattices

Cyclotron resonance measurements have been carried out to evaluate the effective mass of electrons in short-period (GaAs)n/(AlAs)n superlattices (SLs). In order to clarify the Γ-X crossover occurring at n ≈ 12 due to the zone folding effect, we have measured effective masses in SLs with n ranging from 8 to 16 using cyclotron resonance in high magnetic fields (up to 150 T). We found a clear cyclotron resonance in the transmission of 10.61 μm radiation at 99 T in type I SLs (corresponding to an effective mass of 0.098m0 and broad cyclotron resonances at around 90 T in type II SLs in the transmission of 23 μm radiation, which give an effective mass of 0.21 ± 0.01m 0. These resonances were found to be nearly independent of the number of monolayers n.

Investigation of HgSe/HgSe:Fe quantum wells and super lattices

High-field magnetospectroscopy measurements on HgSe/HgSe :Fe quantum wells and superlattices are reported. Fe 2+ substitution of Hg 2+ manifests itself in a donor about 210 meV above the conduction band edge and thus for sufficiently high carrier concentration as a Fermi level pinned system in the mixed valence regime. The MBE-grown samples on ZnTe/GaAs substrates exhibit 2D effects for characteristic well or superlattice dimensions < 20 nm. Strong anisotropy effects due to strain are observed. By variation of the size quantization the predicted transition from a 2D to 3D QHE for Fermi level pinned systems is demonstrated.

Effective mass anisotropy and many-body effects in 2D GaAs/(Ga,Al)As hole gases observed in very high magnetic fields: comparison of theory and experiment

Abstract The effective masses of two-dimensional GaAs/(Ga,Al)As hole systems grown with (100), (311)B, (211)B, (111)B and (110) substrate orientations have been measured in magnetic fields of up to 80 T. The measured anisotropy is discussed in terms of bulk effects using a newly developed theory. Low energy (millimetre wave) cyclotron resonance absorptions show a 15% shift to higher fields in the temperature range 1.4 to 4.2 K over two orders of magnitude of energy. Many-body effects are used to discuss this observation.

Cyclotron Resonance Observation of Heavy and Light Spin Subbands in an Ultra-High Mobility 2D Hole Gas in GaAs/(Al,Ga)As: Evidence for Coupled Magnetoplasmons and Many Body Effects

Many-body effects may be conveniently studied in the two dimensional hole system (2DHS) formed in a GaAs/(Al,Ga)As heterostructure. This 2DHS exhibits extreme valence subband non-parabolicity and a large zero-field splitting of the dispersion relationships of the two spin projections1. In consequence, a complex cyclotron resonance (CR) spectrum might be expected2. However, the experimental study of CR in this Communication shows that such a complex spectrum is in fact absent in most cases. This absence is discussed in terms of a collective cyclotron motion due to Coulomb interactions between holes. Additional evidence for such a collective motion effect is provided by the observation of a very strong temperature dependence of the apparent CR position.

Solid state experiments in megagauss fields

Abstract This paper presents a brief review on recent experiments of solid state physics in very high magnetic fields up to 550 T produced by electromagnetic flux compression and the single-turn coil technique, focusing on magneto-optical spectroscopy in semiconductors, low-dimensional magnetic systems and superconductors. The topics to be discussed include infrared cyclotron resonance in semiconductors, polaron effects in II–VI compounds and the spin splitting in 2D and 3D electron systems of GaAs, the magnetization and the ESR in a spin-Peierls system, CuGeO 3 , and the high frequency conductivity in high- T C superconductors, BiSrCaCuO and YBaCuO.