Novel spontaneous symmetry breaking in metals

Unconventional symmetry breaking without spin order, such as the rotational symmetry breaking (=nematic or smectic) orders as well as the spontaneous loop-current orders, have been recently reported in cuprate superconductors and their related materials. They are theoretically represented by the non-A_1g particle-hole condensation. In this paper, we analyze typical Hubbard models by applying the renormalization-group method and the density-wave equation method, and find that various unconventional orderings emerge due to the quantum interference among spin fluctuations. (author)