Hybrid nodal-chain semimetal with emergent flat band in MgCaN₂

Abstract The distinct over-tiltings of band crossings in topological semimetals generate the type-I and type-II classification Dirac/Weyl nodal-line fermions, accompanied by exotic electronic magnetic transport properties. In this work, we propose a concept hybrid nodal-chain semimetal (NCSM), which is identified linked nodal rings (NRs) hosts inevitable flat band. Using first-principles calculations structure search technique, new ternary nitride MgCaN 2 proposed as first candidate to realize novel 3D NCSM state. Remarkably, emergent along specific direction characteristic signature such nodal-chain, thus offering platform explore interplay between states bands. By analyzing mirror Z invariant developing low-energy effective k ⋅ mathvariant="bold-italic">p model, unveil physical origin with multiple-mirror protected mechanism. Moreover, when NRs are projected onto (010) (001) surfaces, considerable drumhead-like surface can be illustrated unique connection patterns. These results expand our understanding NCSMs from significant tilting effects provide on realizing fermion for further theoretical experimental investigations.