On the nature of the half-integer quantum features on the transport and Hall resistances of 2D electron systems in a quantizing magnetic field

It is shown that in two-dimensional (2D) electron systems in a quantizing m agnetic field, in addition to electron-hole (excitonic) pairing through the Coulomb interaction it is also possible to have Cooper pairing of the 2D e lectrons due to their interaction with 2D phonons and 2D plasmons localized at the interface of the crystals in semiconductor heterostructures. By sum ming the divergent (as T-->0) ladder diagrams in the zero-sound and Cooper channels, the critical temperatures of the transition to the excitonic and Cooper phases are found. It is shown that the excitonic phase can exist onl y in comparatively narrow regions near half-integer values of the filling f actor nu=(2n-1)/2 (n=1,2,3,...), a finding which is in qualitative agreemen t with the experimentally observed anisotropic features in the transport re sistance of 2D systems in the integer quantum Hall effect regime. By taking into account a superposition of states of bound electron pairs and unpaire d 2D electrons in the Cooper phase, one can describe practically all of the experimentally observed quantum features in the fractional quantum Hall ef fect regime, including at values of nu that are not described by the compos ite fermion model. At the same time, the interelectron attraction can promo te triplet Cooper pairing of composite fermions, which is accompanied by th e appearance of an "exotic" quantum feature at nu =5/2. Arguments supportin g the possibility of experimental observation of the Cooper phase are prese nted. (C) 2001 American Institute of Physics.