On Anderson Localisation of Two-Dimensional Electrons in Weak Magnetic   Field
  The two-parameter renormalization group flow diagramme is used for obtaining the magnetic field dependence of localisation length Lc(B) for charged particles in 2D random potential at low disorder and weak magnetic fields B. The result reproduces the periodic singularities of Lc(B). 
D.E.Khmelnitskii (Cavendish Laboratory, University of Cambridge,   Cambridge, UK and Institut Laue-Langevin, Grenoble, FRANCE)