Study of Phonons in the Novel Antiperovskite ZnCNi3

Abstract

The discovery of superconductivity in MgCN_i3 has generated a new puzzle in the recent series of found superconductors. Despite its relatively low T_c ca. 8K, the presence of Ni signals the possible importance of correlation effects which makes the physics of the pairing mechanism relevant to the famous high T_c cuprates and brings the discussion of unconventional non-electron-phonon mechanism. ZnCN_i3 is very similar to MgCN_i3 structurally and having T_c ca. 2K. The lack of superconductivity transition down to 2K is quite unexpected. Understanding why superconductivity is seen in one compound but not the other could be important in resolving the unusual behavior of MgCN_i3. It is, therefore, in the present work, the phonons in ZnCN_i3 are investigated by applying a de Launey angular force constant model. In this model, the relative displacement of the reference atom and one of its neighbors is considered. The calculated zone center phonons and phonon dispersion curves of ZnCN_i3 in the symmetric directions are compared with recently calculated values of MgCN_i3 in order to find the mechanism of superconductivity in these compounds.