Theoretical study of spontaneous symmetry breaking of Fermi surface

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The spontaneous symmetry breaking of the Fermi surface is a new concept found in theory. This symmetry breaking is inferred from recent experiments for bi-layered ruthenates and iron-based and cuprate high-temperature superconductors. Motivated by these experiments we studied the competition with ferromagnetism and other charge orders, a superconducting mechanism due to fluctuations of the orientational symmetry breaking, and Raman scattering which can detect such fluctuations directly. Effects of the fluctuations were explored further by employing a functional renormalization group scheme and scaling theory and we proposed an experimental test for a general property near the phase transition. Ferromagnetic fluctuations were also studied in terms of a functional renormalization group. Finally we achieved a non-perturbative analysis of the one-particle excitation spectrum near the Fermi surface symmetry breaking.