I don't think the attribute table values manifests formatting tags like superscripts. But you format the texts in Labels, Annotations, Legends, etc.
Formatting tags available in ArcMap—Help | ArcGIS for Desktop
Formatting tags can be embedded in the values of the field you use to label a layer's features whether or not you use a label expression. In this way, you can change the format of any portion of a particular value in a label field. To embed formatting tags, the label field must be of string type. Tags and tag attributes used in field values do not need to be surrounded by quotes, so the following are valid values for a label field:
Ls<SUP>-1</SUP>km<SUP>-2</SUP>
Think Location
