Instability of the non-Fermi liquid state of the Sachdev-Ye-Kitaev Model

The Sachdev-Ye-Kitaev (SYK) model is an intriguing 0+1d strongly interacting disordered model of non-Fermi liquid states with exact solution and possible holographic duality. In this talk, I will consider a series of perturbations on the SYK model. We show that the maximal chaotic non-Fermi-liquid phase described by the ordinary SYK model has marginally relevant or irrelevant (depending on the sign of the coupling constants) four-fermion perturbations allowed by symmetry. Changing the sign of one of these four-fermion perturbations leads to a continuous chaotic-nonchaotic quantum phase transition of the system accompanied by a spontaneous time-reversal symmetry breaking. We also studied a generalized 0+1d interacting disordered fermion model which has a series of new fixed points with continuously varying exponents.