IFS=$'\t'
?IFS="\t"
IFS=$'\t'
or POSIX:
IFS="$(printf '\t')"
IFS="\t"
splits on backslash and the letter "t".
IFS=$'\t'
splits on tab.
It's extremely rare to want to split on the letter "n" or "t", rather than linefeed or tab.
See https://github.com/koalaman/shellcheck/wiki/SC1012
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.