How to preserve subscript or superscript formatting in a text string?

I'm reading out some text strings (units) from some Excel files:

filename = 'AAA.xlsx';
opt = detectImportOptions(filename);
opt.VariableUnitsRange = '2:2';      % 2nd row
T1 = readtable(filename, opt);

The problem is that I would have a unit like this: mol kg^-1, and after it is read out, the superscript formatting of "-1" is lost.

Is there an option so that I could preserve the superscript formatting?

Thanks.