Self-assembled structures and devices

Abstract:

The fabrication of three-dimensional photonic crystal structures with sub-micron periodicity was performed by holographic lithography. The photonic crystals of titanium dioxide and polymeric materials were characterized by scanning electron microscopy and optical diffraction measurements. The interference pattern generated at the intersection of four beams from a neodymium laser was employed for the exposure of the photoresist.

Abstract:

We report a remarkably sensitive optical technique for detecting nuclear magnetic resonance from a single ultra-high mobility two-dimensional electron system at a GaAs heterojunction in the fractional quantum Hall regime. Resonant inter-band optical excitation of the 2DES provides a very high degree of dynamic nuclear polarization, three times greater than that previously achieved; this is detected by using inelastic light scattering to measure the Overhauser shift in the energy of the electron spin wave. Our optical detection scheme is sensitive only to the polarization of nuclei in the illuminated volume at the heterojunction. This factor, together with the highly resonant excitation, increases the sensitivity of the technique and has allowed us to measure Knight-shifted magnetic resonance bands of As and Ga nuclei within a single 2DES at filling Factor v = 1/3 at temperatures <100 mK. These measurements can be made over a wide range of temperatures and filling factors and have great potential for the study of collective spin excitations in the fractional quantum Hall regime. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We report resonant inelastic light scattering measurements of collective electronic excitations at filling factor v = 1/3 in a high mobility 2DES at temperatures between 50 mK and 3 K. In a narrow range of temperatures near 1 K the intensity of light scattering from the charge density mode, and the exchange enhancement of the energy of a collective spin excitation, fall rapidly to zero. We deduce that the electron correlation characteristic of the spin-polarized electron liquid at v = 1/3 collapses at 1 K: this collapse is triggered by thermal fluctuations of the electron spin. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We present measurements of photoluminescence from the incompressible two-dimensional electron system at filling factor v = 1. By varying the doping density, sample structure and angle between magnetic field and confinement plane we investigate the influence of electron-electron and electron-valence hole interactions on the photoluminescence spectrum. We find that a strong electron-valence hole interaction suppresses a characteristic discontinuity in the photoluminescence energy. In all samples studied the electron-valence hole interaction is strong enough to prevent observation of a theoretically predicted tilt-induced shrinkage of skyrmion-charged spin texture excitations. (C) 1998 Elsevier Science B.V. All rights reserved.