Shining light on electrons under extreme conditions

Strongly-correlated two-dimensional (2D) electron fluids occur in artificial semiconductor heterostructures of high perfection that are subjected to quantizing magnetic fields. Under conditions of high magnetic fields, low temperatures in the millikelvin range and low electron density, the 2D quantum fluids display dispersive low-energy collective excitations that represent time- and space-dependent oscillations in the charge and/or the orientations of spin. These collective modes manifest fundamental interactions that are responsible for electron correlation. Studies of low-lying collective excitation modes play pivotal roles in the low-temperature phases of the electron liquids and offer venues of studying energetics, coherence, magnetization, instabilities and quantum phase transitions of the 2D system. In 1978 a proposal by Burstein, Pinczuk and Buchner suggested that resonant inelastic light scattering methods would have the sensitivity required to Study elementary excitations of 2D electron systems in semiconductors. We review here recent light scattering results obtained from 2D electron fluids in semiconductor quantum structures under extreme conditions of low temperature and large magnetic field. In these experiments, resonant inelastic light scattering methods probe fundamental behaviors due to interactions with a sensitivity that will keep light scattering studies at the frontiers of research of quantum fluids in low dimensional electron systems. (C) 2005 Elsevier Ltd. All rights reserved.