Ideal Inner Nodal Chain Semimetals in Li₂XY (X = Ca, Ba; Y = Si, Ge) Materials

The chain-type nodal loops in the reciprocal space can generate exotic nodal chain fermions. Here, we report that Li₂XY (X = Ca, Ba; Y = Si, Ge) compounds are ideal inner nodal chain semimetals. Their band structures are composed of two connecting nodal loops with either hybrid or type-I band dispersion. The signatures of the nodal chain, such as the nontrivial surface states, are quite pronounced in these Li₂XY compounds, since there is only a single inner nodal chain without other extraneous bands near the Fermi level. These compounds are existing materials and ambient-stable, which is available to realize the experimental detection of inner nodal chain fermions or further the practical applications.