Fractional quantum Hall effect in second subband of a 2DES

¹ Departamento de Física, Universidade Federal do Paraná - CP 19044, CEP 81531-990, Curitiba, PR, Brazil
² Instituto de Física, Universidade Federal de Alagoas - 57072-970, Alagoas, Brasil
³ Instituto de Física da Universidade de São Paulo - CP 66318, CEP 05315-970, São Paulo, SP, Brazil
⁴ Institute of Semiconductor Physics - Novosibirsk, 630090, Russia
⁵ GHMFL-CNRS - BP-166, F-38042 Grenoble Cedex 9, France, EU
⁶ INSA-Toulouse - F-31077 Toulouse Cedex 4, France, EU
⁷ Institut Universitaire de France - Toulouse, France, EU

^a celso@fisica.ufpr.br

Received: 25 November 2010
Accepted: 26 March 2011

Abstract

In the present paper we report on the experimental electron sheet density vs. magnetic field diagram for the magnetoresistance R_xx of a two-dimensional electron system (2DES) with two occupied subbands. For magnetic fields above 9 T, we found fractional quantum Hall levels centered around the filing factor ν=3/2 in both the two occupied electric subbands. We focused specially on the fractional levels of the second subband, whose experimental values of the magnetic field B of their minima do not obey a periodicity law in 1/|B−B_c|, where B_c is the critical field at the filling factor ν=3/2, and we explain this fact entirely in the framework of the composite fermions theory. We use a simple theoretical model to give a possible explanation for the fact.