Universal conductance fluctuations in a parabolic quantum well tunable from two- to three-dimensional behavior

Parabolic quantum wells (PQWS) allow the study of the transition between th e quantum limit with one two-dimensional (2D) subband occupied and the case of two occupied subbands. During this transition the character of phase co herent loops is changed from being strictly 2D to three-dimensional (3D). T he implications for the amplitude and correlation field of universal conduc tance fluctuations (UCF) were studied experimentally. The population of the second subband is found to manifest itself in both quantities. Possible in fluences of increased electron-electron scattering and elastic intersubband scattering are discussed. (C) 1998 Elsevier Science B.V. All rights reserv ed.