New results at half-fillings in the second and third Landau level

This paper presents some recent results on the anisotropic electronic trans port at half-filling factors in the second and third Landau levels. In the third Landau level at v = (9)/(2) and (11)/(2), the electronic transport is already strongly anisotropic in perpendicular magnetic field. This anisotr opic phase is believed to be due to the formation of a unidirectional charg e density wave. Applying an in-plane field overcomes the initial pinning an d reorients the direction of this anisotropy. In the second Landau level, t he even-denominator fractional quantum Hall state at v = (5)/(2) and (7)/(2 ) is destroyed and transformed into an anisotropic phase by an in-plane mag netic held. This result provides additional evidence that the ground state at v = (5)/(2) and (7)/(2) is spin-polarized. (C) 2001 Elsevier Science B.V . All rights reserved.