Prediction of two-dimensional Cu2C with polyacetylene-like motifs and Dirac nodal line

Abstract

The design of novel two-dimensional (2D) materials with unique atomistic configurations and exotic properties are highly desirable for material science. Here, we report the prediction of 2D ${\mathrm{Cu}}_{2}\mathrm{C}$ layers featuring unique carbon motifs with Dirac nodal lines through evolutionary algorithm searches in conjunction with first-principles calculations. The global minimum $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Cu}}_{2}\mathrm{C}$ is an exciting new structure featuring one-dimensional (1D) zigzag carbon chains sandwiched by two hexagonal-close-packed copper monolayers, conferring to our predicted ground-state 2D $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Cu}}_{2}\mathrm{C}$ an inverse coordination structure. This polyacetylene-like motif $(\mathrm{poly}\text{\ensuremath{-}}{\mathrm{C}}_{2})$ is also encountered in $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Cu}}_{2}\mathrm{C}$. Remarkably, the electronic band structure of $\ensuremath{\alpha}$ and $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Cu}}_{2}\mathrm{C}$ phases containing polyacetylene-like chains display a 1D Dirac nodal line, which is protected by the glide plane symmetry. Fermi velocities $({v}_{f})$ as high as $2.45\ifmmode\times\else\texttimes\fi{}{10}^{5}$ and $3.85\ifmmode\times\else\texttimes\fi{}{10}^{5}$ m/s are calculated for $\ensuremath{\alpha}$ and $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Cu}}_{2}\mathrm{C}$ phases, respectively. This work is an effective effort to design and stabilize the 2D copper carbide layers with exotic structures and nodal lines.