usepackage{sourcecodepro}

usepackage{fontspec}
setmonofont{Source Code Pro}

documentclass[11pt]{article}
usepackage{sourcecodepro}
begin{document}
begin{verbatim}
β
â
β̂
end{verbatim}
end{document}

documentclass[11pt]{article}
usepackage{fontspec}
setmonofont{Source Code Pro}
begin{document}
begin{verbatim}
β
â
β̂
end{verbatim}
end{document}