Can't display entries within Subcategory

Hi there,

I'm trying to display subcategory entries from a specific category and can't seem to figure it out. Here's what I have outlined within my categories:

New York (category)
-- Articles (subcategory)

Florida (category)
-- Articles (subcategory)

As you can see, all of my main categories share the same name of its subcat - in this case "Articles".

I've tried the following and it doesn't seem to be working for me:

<mt:Entries category="New York/Articles" sort_by="authored_on" sort_order="descend">
<em><$mt:EntryExcerpt$></em>
</mt:Entries>

Any ideas? I'm stumped!

Thanks in advance.