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

This paper presents some recent results on the anisotropic electronic transport 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 anisotropic phase is believed to be due to the formation of a unidirectional charge density wave. Applying an in-plane field overcomes the initial pinning and reorients the direction of this anisotropy. In the second Landau level, the 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 magnetic field. 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.