begin{equation*}
    U^{k} = begin{tikzpicture}
            matrix [matrix of math nodes,left delimiter=(,right delimiter=)] (m)
            {
                z^{k}     &  0 & cdots & s z^{0} & s z^{1} & cdots & s z^{k-2} & s    z^{k-1} \
                z^{k-1} s &  vdots&    & -overline{z} & s^{2} z^{0}   & cdots & s^{2} z^{k-3} & s^{2} z^{k-2} \
                z^{k-2} s &   & &  & -overline{z} & s^{2} z^{0} & cdots & s^{2} z^{k-3} \
                vdots    &   & &  &   & ddots & ddots & vdots \
                z s       & vdots&  &   & 0 &   & -overline{z} & s^{2} z^{0} \
                s         & 0 & cdots &  &   &   &   & -overline{z} \
                0         & 1 &   & 0 &  &  &   &   \
                vdots    &   & ddots & &  &   & 0 &   \
                0         & 0 &   & 1 &  & &   &   \
            };
            draw (m-2-4.north west) rectangle (m-6-8.south east);
            draw (m-7-2.north west) rectangle (m-9-4.south east);
            end{tikzpicture}
end{equation*}