Topological type-II nodal line semimetal (NLS) was proposed quite recently and exhibits distinct properties compared with conventional type-I NLS. To date, no ambient-condition stable candidate material has been reported. Here we propose that a stable Kagome compound MgBi can host a type-II nodal line state with the protection of time reversal and spatial inversion symmetries. Similar to type-I NLSs, the type-II nodal line in MgBi is characterized by the drumhead surface states, which has not been observed in the previous type-II NLSs. The nodal line in MgBi can open a minor gap, and a pair of 3D Dirac points occurs when SOC is included. The SOC-induced gap around the nodal line is quite small, and the formation of 3D Dirac points is independent of the nodal line. Therefore, the MgBi compound is expected to be a good candidate to investigate the exotic properties of both type-II NLS and 3D Dirac semimetal states.

We study the electronic structures and magnetic properties of Mn 2 CoZ ͑Z =Al,Ga,In,Si,Ge,Sn,Sb͒ compounds with Hg 2 CuTi-type structure using first-principles full-potential linearized-augmented plane-wave calculations. It is found that the compounds with Z = Al, Si, Ge, Sn, and Sb are half-metallic ferrimagnet. Experimentally, we successfully synthesized the Mn 2 CoZ ͑Z =Al,Ga,In,Ge,Sn,Sb͒ compounds. Using the x-ray diffraction method and Rietveld refinement, we confirm that these compounds form Hg 2 CuTi-type structure instead of the conventional L2 1 structure. Based on the analysis on the electronic structures, we find that there are two mechanisms to induce the minority-spin band gap near the Fermi level, but only the d-d band gap determines the final width of the band gap. The magnetic interaction is quite complex in these alloys. It is the hybridization between the Mn͑C͒ and Co atom that dominates the magnitude of magnetic moment of the Co atom and the sign of the Mn͑B͒-Co exchange interaction. The Mn 2 CoZ alloys follow the Slater-Pauling rule M H = N V − 24 with varying Z atom. It was further elucidated that the molecular magnetic moment M H increases with increasing valence concentration only by decreasing the antiparallel magnetic moment of Mn͑C͒, while the magnetic moments of Mn͑B͒ and Co are unaffected.

We present a rational design scheme intended to provide stable high spin polarization at the interfaces of the magnetoresistive junctions by fulfilling the criteria of structural and chemical compatibilities at the interface. This can be realized by joining the semiconducting and half-metallic Heusler materials with similar structures. The present first-principles calculations verify that the interface remains half-metallic if the nearest interface layers effectively form a stable Heusler material with the properties intermediately between the surrounding bulk parts. This leads to a simple rule for selecting the proper combinations.

We propose for the first time the concept and properties of topological electride materials.

NaAlSi manifests both topological band structures and superconductivity, which is promising to realize a topological superconducting state.