I want the graph’s title to show “the title is m0”, in which 0 is placed as a subscript next to “m”. I am using the expression() but it works without other characters, while fail to make it a subscript when other characters are present. How can we fix this?

data("iris")

ggplot(data=iris,mapping=aes(x=Petal.Length,y=Petal.Width,color=Species))+
    geom_point()+
    geom_smooth(method="lm") +
    labs(title = paste0("the title is ", expression(m[0])))

The resulting graph looks like

See that the title does not give what I want by displaying [0] rather than 0 (subscript).