Insert two images as subfigures vertically

Question

I'm using Revtex 4.1 and would like to insert two images to appear as subfigures. I would like them to have labels a) and b). I've no idea how to do this in Revtex and the minipage idea below (from an answer to a similar question on Stackexchange) didn't work.

\begin{figure}
\subfloat[Fig6a.pdf]{
\begin{minipage}[c][1\width]{0.5\textwidth}%
\includegraphics[clip,width=1\textwidth]{Fig6a.pdf}%
\end{minipage}}
\subfloat[Fig6b.pdf]{\centering{}%
\begin{minipage}[c][1\width]{0.5\textwidth}%
\begin{center}
\includegraphics[clip,width=0.6\textwidth]{Fig6b.pdf}
\par\end{center}%
\end{minipage}}
\caption{main caption}
\end{figure}

Answer 1

You need no fancy minipage; the code you're using is for ensuring the two subcaptions are at the same vertical level, with the subfloats side by side.

\documentclass[twocolumn]{revtex4-1}

\usepackage{graphicx}
\usepackage[caption=false]{subfig}

\usepackage{lipsum} % just for the example

\begin{document}

\lipsum[1-2]

\begin{figure}[htp]

\subfloat[Fig6a.pdf]{%
  \includegraphics[clip,width=\columnwidth]{example-image-a}%
}

\subfloat[Fig6b.pdf]{%
  \includegraphics[clip,width=0.6\columnwidth]{example-image-b}%
}

\caption{main caption}

\end{figure}

\lipsum

\end{document}