title: Superscript in R
body: <p>How do I superscript the units this axis title. The <code>""</code> represent the parts that I need to be superscripted: <code>Photosynthetically available radiation (µE m"-2"d"-1")</code>.</p>
  
  <p>I have used the formula and having no luck so far:</p>
  
  <pre><code>plot(PAR~SST,data=brazilw, pch=15,col="red", main ="Fig. 1. Relationship between photosynthically available radiation\n and sea surface temperature",
  ylab=expression("Photosynthetically available radiation (µE m"^-2~d^-1))
  </code></pre>