How to have a big sigma and big zero inside the whole matrix

How can I achieve the following big sigma and big zero in a matrix: Each of the symbols are there in place of a group of matrix elements and not one element. Suppose we divide matrix into two sections (column-wise), one section is called $\sigma$ and the other is showing that all elements are zero (hence a bog zero). So the following small equation is not what I need:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
$\begin{bmatrix}\sum 0 \end{bmatrix}$
\end{document}
• \LARGE, \huge and similars are not working? – Guilherme Zanotelli Sep 19 '16 at 5:14
• Are you looking for \displaystyle\sum? – Heiko Oberdiek Sep 19 '16 at 5:41
• You should use \Sigma not \sum e.g. \begin{bmatrix}\Sigma & 0 \end{bmatrix} and it would help if you explained why you don't need your mwe. – Manuel Schmidt Sep 19 '16 at 5:43
• Edited the question to add more details of what the desired output should be and what it looks like. @ManuelSchmidt – Gigili Sep 19 '16 at 5:59
• @HeikoOberdiek Edited the question. Hope it is clear now. – Gigili Sep 19 '16 at 6:00

Something like the following, maybe? (Feel free to change the sizes of the symbols by adjusting the first argument of the \scalebox directives.) \documentclass{article}
\usepackage{amsmath}  % for 'bmatrix' environment
\usepackage{graphicx} % for '\scalebox' macro
\newcommand\humongousZero{\scalebox{3}{$0$}}
\newcommand\humongousSigma{\scalebox{3}{$\Sigma$}}

\begin{document}
$abc \begin{bmatrix} & & & & \\ & \humungousSigma & & \humungousZero & \\ & & & & \end{bmatrix} xyz$
\end{document}

Is this what you are looking for?

\documentclass{article}
\usepackage{amsmath}

\newcommand\bigZero{\mbox{\huge$0$}}
\newcommand\bigSigma{\mbox{\huge$\Sigma$}}
\begin{document}
$\begin{bmatrix} \bigSigma & \bigZero \end{bmatrix}$
\end{document}

For getting arbitrary font size, you can extend the definition, but you also need to enable arbitrary font scaling.

\RequirePackage{fix-cm}

\documentclass{article}
\usepackage{amsmath}

\DeclareFontShape{OMX}{cmex}{m}{n}{
<-7.5>    cmex7
<7.5-8.5> cmex8
<8.5-9.5> cmex9
<9.5->    cmex10
}{}

\newcommand\bigZero{\mbox{\fontsize{#1}{0}\selectfont$0$}}
\newcommand\bigSigma{\mbox{\fontsize{#1}{0}\selectfont$\Sigma$}}
\begin{document}
$A=\begin{bmatrix} \bigSigma & \bigZero \end{bmatrix}\qquad B=\begin{bmatrix} \bigSigma & \bigZero \end{bmatrix}$
\end{document} • Sort of. Couldn't it get any bigger than that? A big $m \times n$ matrix? – Gigili Sep 19 '16 at 6:26