Absolute stability region
Stable region in red.

Coefficients

\begin{align} \begin{array}{c|cc} - \frac{\sqrt{3}}{6} + \frac{1}{2} & \frac{1}{4} & - \frac{\sqrt{3}}{6} + \frac{1}{4}\\ \frac{\sqrt{3}}{6} + \frac{1}{2} & \frac{1}{4} + \frac{\sqrt{3}}{6} & \frac{1}{4}\\ \hline & \frac{1}{2} & \frac{1}{2} \end{array}\end{align}

Properties