You may insert HTML tags directly to Markdown documents. To toggle the "superscripting" mode, use sup
.
MyTitle
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J.Smith<sup>1</sup>, K.John<sup>2</sup>, H.Gone<sup>*</sup>.
EDIT: You may also use round brackets to indicate exactly the part of text to be reformatted.
J.Smith^(1), K.John^(2), H.Gone^(*)
EDIT: This has changed for Markdown V2
2^10
2^(10)
2^10^
2^(10)^