Possible instabilities in quadratic and cubic nodal-line fermion systems with correlated interactions

Abstract

Influence of short-range four-fermion interactions on quadratic and cubic nodal line fermion systems is studied by renormalization group theory. It is found that arbitrarily weak four-fermion interaction could drive quadratic or cubic nodal line fermion system to a new phase. According to the initial conditions and value of fermion flavor, the system may appear three kinds of instabilities. First, quadratic or cubic nodal line is split into conventional nodal lines, thus the system becomes nodal line semimetal. Second, finite excitonic gap is generated, and the system becomes an excitonic insulator. Third, the system is driven into superconducting phase. Thus, quadratic and cubic nodal line fermion systems are rare strong correlated fermion systems in three dimension under the influence of four-fermion interactions. These theoretical results may be verified in the candidates for quadratic and cubic nodal line fermion systems.