Composite charge order in the pseudogap region of the cuprates
  We study the Ginzburg-Landau free energy functional for two coupled U(1) charge order parameters describing two non-equivalent charge orders with wave vector ${\bf Q}$ detected in X-ray and STM measurements of underdoped cuprates. We do not rely on a mean-field analysis, but rather utilize a field-theoretical technique suitable to study the interplay between vortex physics and discrete symmetry breaking in two-dimensional systems with U(1) symmetry. Our calculations support the idea that in the clean systems there are two transitions: from a high temperature disordered state into a state with a composite charge order which breaks time-reversal symmetry, but leaves U(1) fields disordered, and then into a state with quasi long range order in the U(1) fields. 
A. M. Tsvelik and A. V. Chubukov
cond-mat.supr-con