Prediction of Ideal Topological Semimetals with Triply Degenerate Points in the NaCu_{3}Te_{2} Family.

Triply degenerate points (TDPs) in band structure of a crystal can generate novel TDP fermions without high-energy counterparts. Although identifying ideal TDP semimetals, which host clean TDP fermions around the Fermi level (E_{F}) without coexisting with other quasiparticles, is critical to explore the intrinsic properties of this new fermion, it is still a big challenge and has not been achieved up to now. Here, we disclose an effective approach to search for ideal TDP semimetals via selective band crossing between antibonding s and bonding p orbitals along a line in the momentum space with C_{3v} symmetry. Applying this approach, we have successfully identified the NaCu_{3}Te_{2} family of compounds to be ideal TDP semimetals, where two, and only two, pairs of TDPs are located around the E_{F}. Moreover, we demonstrate a fundamental mechanism to modulate energy splitting between a pair of TDPs, and we illustrate the intrinsic features of TDP Fermi arcs in these ideal TDP semimetals.