If you are using R2014b or later, then use char(8364) if you are using the default 'interpreter', 'none' or if you are using 'interpreter', 'tex'.
However, if this needs to go into a string with 'interpreter', 'latex' then you are going to have a problem -- unless it happens that the rest of the string does not include any \ directives (... in which case the interpreter did not need to be set to 'latex' anyhow.) It is not known if there is any way to add any optional packages for use with latex in the last couple of releases of MATLAB; there was an obscure way in some of the releases from R2014b to perhaps R2016a or so.
