Plotting with basic plot

When I run this code fragment

x <- (0:100)/100
y <- x^2
plot(x,y,type="l",xlab=expression(x),ylab=expression(f(x)==x^2),
  main="Quadratfunktion")

the exponent on the y-axis label is mutilated.
How can the be changed with minimal effort?

ggplot2
 does not have this problem:

library(ggplot2)
x <- (0:100)/100
y <- x^2
qplot(x,y,geom="line",xlab=expression(x),ylab=expression(f(x)==x^2),
  main="Quadratfunktion")