Theory of charge loop current in quasi-one-dimensional systems based on functional renormalization group study

Various symmetry-breaking phenomena are the central issues in strongly correlated metals. For instance, violations of C_{4} rotational symmetry in tetragonal systems, so called the quantum liquid phase, has been intensively studied on Fe-, Cu-based and heavy fermion superconductors. One of the origin of the symmetry breaking is spontaneous current phase due to odd-parity loop current (LC) ordering. Until now, various types of LC orders, like the ferro-LC order along Cu-O and O-O bonds and the antiferro-LC order along Cu-Cu bonds have been discussed. Here, we study spin-fluctuation-driven LC order mechanism based on the functional renormalization group (fRG) theory. Our proposed mechanism leads to the ferro LC order in a quasi-one-dimensional systems, which accompanies the magnetic field that is measurable experimentally.