Topological skyrmion pseudogap in the cuprate superconductors

We consider a theory for the formation of the pseudo-gap in the underdoped region of cuprate superconductors, in which there is a large regime of fluctuations between the d-wave SC order and d-wave charge density modulations. These fluctuations involve the phase as well as the amplitude of each order parameter and can be described within an emerging SU(2) symmetry. The theory captures large part of the phenomenology of the cuprates. We will discuss experimental prediction of this theory, including the presence of collective modes and the generation of unusual topological defects in the pseudo-spin space. We will outline the differences between the SU(2) fluctuation approach to strong coupling scenarios involving the fractionalization of the electron.