How broad should the research Interests of an undergraduate applying for grad school be? I'm an undergraduate student applying to grad school. In my Research Interests section in my CV (or somewhere else), I wonder how broad should my interests be.

For example, I have worked on topics about plasmonics that fall under condensed matter physics. Now can I write condensed matter physics as a research interest? I actually like most of subjects in condensed matter physics, and have quite accidentally worked on this specific subject plasmonics. Limiting the research interests to just plasmonics may limit my choices for application, while being too broad may cause me look like someone who has not even explored current research areas.

As an applied physics and engineering student, how broad should by research interests appear on my application?
I personally make it a little more specific to the department. Something like, "condense matter physics, in particular, the faculty Prof. A and Prof. B looks interesting in that (etc)."