ABSTRACT

This chapter presents the nonlinear σ-model (NLσM) approach and derive general renormalization group equations in one-loop approximation in the case when an electron is characterized by both spin and isospin. It offers general results for the description of low-temperature transport in a two dimensional (2D) two-valley electron system in a Si-metal-oxide-semiconductor field-effect transistor (MOSFET) in the presence of spin and valley splittings. The chapter explains transport experiments in a 2D electron system in a double-quantum-well heterostructure with common scatterers. In a double-quantum-well heterostructure with common scatterers for electrons one can expect behavior of resistivity similar to the one in a Si-MOSFET. Control of electron concentration in one quantum well by gate voltage allows to interpolate between the case of equal electron concentrations in each quantum well and the case in which one quantum well is empty. In the orthogonal symmetry class, contribution to the conductance due to strong electron-electron interaction is of opposite sign with respect to weak localization contribution.