EDGE CHANNELS IN INTEGER AND FRACTIONAL QUANTUM-HALL REGIME INVESTIGATED BY MAGNETOCAPACITANCE

We have evaluated the width of edge channels in the fractional and int eger quantum-Hall (QH) regime by the magnetocapacitance measurement be tween a gate and two-dimensional electron system in GaAs/AlGaAs hetero structures. The frequency dependence of the magnetocapacitance between 100 Hz and 1 MHz has been measured at temperatures between 35 mK and 0.4 K. At the fractional QH regime, the total width of the edge channe ls is found to be 2.5 and 9 mu m at 35 mK at the QH plateaux of fillin g factor v = 1/3 and 2/3, respectively. In the integer QH regime, the temperature dependence of the edge channel width is almost flat in the range of 35 mK-0.4 K. At the QH plateau of v = 1 due to spin-splittin g Landau level, the width of total edge channel is almost the same val ue with that at v = 2. The width at v = 3 is also comparable to that a t v = 4, although the residual bulk conductivity of v = 3 is an order of magnitude larger than that of v = 4. (C) 1998 Elsevier Science B.V. All rights reserved.