\documentclass{article}
\usepackage{amsmath, amsfonts}
\usepackage{tikz}

\begin{document}
\begin{center}
    \begin{tikzpicture}[scale=0.5]
    \draw[dashed] (0, -1) -- (0, 1);
    \draw[->] (-1, 0) -- (1, 0);
    \draw (0.75, 1.25) node[left, below]{$\mathcal{L}$};
\end{tikzpicture}
\end{center}
    
\end{document}