APS uses the normal delimiter $ for any TeX in-line math, e.g.,
the quantityis obtained from the input
the quantity $a^{z}$
TeX will assume that you want a superscript or subscript to consist of the first token (generally a single character or command) following the _ or , unless you use curly brackets to delimit a subscript/superscript. It is safest to use the curly brackets if unsure. We have followed this convention in this guide. Again, don't use any vertical motion commands in math; horizontal motion commands should be unnecessary as well.