In ordinary / the placement of root indices is sometimes not so
good: 
(|[]k|). In the
amsmath package leftroot and uproot allow you to adjust
the position of the root:
\sqrt[\leftroot{-2}\uproot{2}\beta]{k}
will move the beta up and to the right:
. The negative argument used
with leftroot moves the 
to the right. The units are a small
amount that is a useful size for such adjustments.