How to use superscript in a ggplot title with greek letter

Question

How to write a greek letter (tau) with a superscript in a title with ggplot? I tried as follows:

cor <- cor(H2ORateTau[,"Tau"],H2ORateTau[,"Rate"])

ggplot(data = H2ORateTau, aes(x=Tau,y=Rate)) +
  
  geom_point(col="red",size=1.5)+  
  
  geom_smooth(method="lm", se=TRUE) +
  
  labs(title=expression(paste(Rate of decay vs tau^2)),subtitle=paste("Water Correlation Coefficient :",round(cor,digits=4)),
       y=expression(paste("R"["2obs"]*"(ms"^"-1"*")")), x=expression(paste(tau^2, (ms^2)))) +
 
  theme_bw()

I do not understand why expression(paste()) works for x label and not for title... Any hint will be appreciated.

Answer 1

Try this with your data:

#Code
ggplot(data = iris, aes(x=Sepal.Length,y=Sepal.Width)) +
  geom_point(col="red",size=1.5)+  
  geom_smooth(method="lm", se=TRUE) +
  labs(title=expression(Rate~of~decay~vs~tau^2),
       subtitle=paste("Water Correlation Coefficient :",round(cor,digits=4)),
       y=expression(paste("R"["2obs"]*"(ms"^"-1"*")")), x=expression(paste(tau^2, (ms^2)))) +
  theme_bw()

Output:

Your code would look like this (not tested as no data was shared):

#Code
ggplot(data = H2ORateTau, aes(x=Tau,y=Rate)) +
  geom_point(col="red",size=1.5)+  
  geom_smooth(method="lm", se=TRUE) +
  labs(title=expression(Rate~of~decay~vs~tau^2),
       subtitle=paste("Water Correlation Coefficient :",round(cor,digits=4)),
       y=expression(paste("R"["2obs"]*"(ms"^"-1"*")")), x=expression(paste(tau^2, (ms^2)))) +
  theme_bw()