Using f$^6$
is not the best way to cope with this, because it's not math, so
f\textsuperscript{6}
would be a better way. The problem is that the character “f” slightly extends beyond its bounding box. There is a built-in mechanism for coping with this, the italic correction that, despite its name, can come to rescue also for non slanted fonts, which are the ones where the problem presents more often.
Unfortunately, \textsuperscript
doesn't add the italic correction, which it should, in my opinion. More unfortunately, patching \textsuperscript
is not sufficient for footnotes.
Let's do a test document:
\documentclass{article}
\begin{document}
f\textsuperscript{6} f\textsuperscript{1} y\textsuperscript{6}
f\footnote{A}
f\footnote{B}
f\footnote{C}
f\footnote{D}
f\footnote{E}
f\footnote{F}
\setcounter{footnote}{0}
y\footnote{A}
y\footnote{B}
y\footnote{C}
y\footnote{D}
y\footnote{E}
y\footnote{F}
\end{document}
that outputs

Now we patch \textsuperscript
and \footnote
; actually a couple of internal macros need to be patched.
\documentclass{article}
\usepackage{etoolbox}
\makeatletter
\pretocmd\@textsuperscript{\/}{}{}
\patchcmd\@footnotemark{\edef}{\/\edef}{}{}
\makeatother
\begin{document}
f\textsuperscript{6} f\textsuperscript{1} y\textsuperscript{6}
f\footnote{A}
f\footnote{B}
f\footnote{C}
f\footnote{D}
f\footnote{E}
f\footnote{F}
\setcounter{footnote}{0}
y\footnote{A}
y\footnote{B}
y\footnote{C}
y\footnote{D}
y\footnote{E}
y\footnote{F}
\end{document}
and we get

You can see that the output with y
is unaffected, while it's improved for f
, because we essentially add \/
before \textsuperscript
and \footnote
. If the font is properly designed, the italic correction should compensate the right amount of spacing.
A possible patch for \supercite
is
\patchcmd{\mkbibsuperscript}{\unspace}{\unspace\/}{}{}
Example.
\documentclass{article}
\usepackage{biblatex}
\makeatletter
\pretocmd\@textsuperscript{\/}{}{}
\patchcmd\@footnotemark{\edef}{\/\edef}{}{}
\patchcmd{\mkbibsuperscript}{\unspace}{\unspace\/}{}{}
\makeatother
\addbibresource{xampl.bib}
\begin{document}
\nocite{*}
f\supercite{article-full}
\printbibliography
\end{document}

f\/\textsuperscript{6}
– egreg May 27 '14 at 15:30