  We demonstrate unexpected occurrence of linear bands resembling Dirac cone at
the zone-center of Au$_2$Sn surface alloy with $\left( \begin{smallmatrix}
2&1\\ 1&3 \end{smallmatrix} \right)$ surface structure formed by deposition of
about 0.9 ML Sn on Au(111) at elevated temperature. The surface exhibits an
oblique symmetry with unequal lattice constants making it the first two
dimensional surface alloy to exhibit Dirac cone with a non-honeycomb lattice.
