Spin rotational symmetry breaking by orbital current patterns in two-leg ladders

We investigate the physical consequences of orbital current patterns (OCP) in doped two-leg Cu-O Hubbard ladders. The internal symmetry of the pattern, in the case of the ladder structure, differs slightly from that suggested so far for cuprates. We focus on this OCP and look for measurable signatures of its existence. We compute the magnetic field produced by the OCP at each lattice site and estimate its value in view of a possible experimental detection. Using a renormalization-group (RG) analysis, we determine the changes that are caused by the SU(2) spin rotational symmetry breaking which occurs when the OCP is present in the ground-state phase diagram. The most significant one is an in-plane spin-density wave gap opening in an otherwise critical phase, at intermediate dopings. We estimate the value of this gap, give an analytic expression for the correlation functions and examine some of the magnetic properties of this new phase which can be revealed in measurements. We compute the conductance in the presence of a single impurity using an RG analysis. A discussion of the various sources of SU(2) symmetry breaking underscores the specificity of the OCP-induced effects.