Typing block matrices with zero blocks and separators

Question

Is there a way to type something like (sorry for the strange picture)

using pmatrix or another method as simple as that? Thanks in advance.

p.s.

I'm able to create

using

\newcommand\bigzero{\makebox(0,0){\text{\huge0}}}
\begin{equation}
\begin{pmatrix}
\begin{matrix} a & b \\ c & d \end{matrix} & \bigzero \\ \bigzero & \begin{matrix} a & b \\ c & d \end{matrix}
\end{pmatrix}
\end{equation}

but I can't type the separators. I know it (and much more complex forms) can be typed using array command, but I want to use the simple matrix commands if possible.

Answer 1

Update (2023)

With nicematrix it's really easy.

\documentclass{article}
\usepackage{amsmath}
\usepackage{nicematrix}

\begin{document}

\[
\begin{pNiceArray}{cc|cc}
  a & b & \Block{2-2}<\Large>{\mathbf{0}} \\
  c & d \\
  \hline
  \Block{2-2}<\Large>{\mathbf{0}} && a & b \\
  && c & d
\end{pNiceArray}
\]

\end{document}

Original answer (2016)

Not many possibilities without explicitly using array, I'm afraid:

\documentclass{article}
\usepackage{amsmath}

\newcommand{\bigzero}{\mbox{\normalfont\Large\bfseries 0}}
\newcommand{\rvline}{\hspace*{-\arraycolsep}\vline\hspace*{-\arraycolsep}}

\begin{document}

\[
\begin{pmatrix}
  \begin{matrix}
  a & b \\
  c & d
  \end{matrix}
  & \rvline & \bigzero \\
\hline
  \bigzero & \rvline &
  \begin{matrix}
  a & b \\
  c & d
  \end{matrix}
\end{pmatrix}
\]

\end{document}

With array:

\documentclass{article}
\usepackage{amsmath}

\newcommand{\bigzero}{\mbox{\normalfont\Large\bfseries 0}}

\begin{document}

\[
\left(\begin{array}{@{}c|c@{}}
  \begin{matrix}
  a & b \\
  c & d
  \end{matrix}
  & \bigzero \\
\hline
  \bigzero &
  \begin{matrix}
  a & b \\
  c & d
  \end{matrix}
\end{array}\right)
\]

\end{document}