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

Abstract

We study a series of perturbations on the Sachdev-Ye-Kitaev (SYK) model. We show that the maximal chaotic non-Fermi-liquid phase described by the ordinary $q=4$ 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. Starting with the ${\mathrm{SYK}}_{q}$ model with a $q$-fermion interaction, similar perturbations can lead to a series of new fixed points with continuously varying exponents.