No, but you can easily copy the one from Word - right click Word's
superscript icon, and choose Properties. From the dropdown next to the
icon, choose Copy Button Face. In XL, select the button you want to have
the superscript icon, right-click, choose properties, and, from the
dropdown next to the icon, choose Paste button face.
You could also do it via VBA:
Commandbars("MyBar").Controls("MyButton").FaceID = 57
See John Walkenbach's FaceID macro:
http://j-walk.com/ss/excel/tips/tip67.htm