On the mass enhancement near optimal doping in high magnetic fields in   the cuprates
  Recent observation of a mass enhancement in high magnetic fields in nearly optimally doped cuprates poses several puzzles. For the suggested nodal electron pocket induced by bidirectional charge order in high field, we propose that the mass enhancement is very anisotropic around the small Fermi surface. The corners of the pocket are proposed to have a big enhancement without any enhancement along the diagonal nodal direction. A natural mechanism for such angle dependent mass enhancement comes from the destruction of the Landau quasiparticle at hot spots on the large Fermi surface at a proximate quantum critical point. The possibility of a divergent cyclotron effective mass is discussed within a scaling theory for such a quantum critical point. We consider both a conventional quantum critical point associated with the onset of charge order in a metal and an unconventional one where an antinodal pseudogap opens simultaneously with the onset of charge order. The latter may describe the physics of the strange metal regime at zero magnetic field. 
T. Senthil
cond-mat.str-el