David Haberstich is correct...you can certainly write your dissertation on
contemporary art but some places are better than others to do it.

My alma mater, the Institute of Fine Arts (New York University) has both
Kirk Varnedoe and Robert Rosenblum on the faculty and either would be an
excellent thesis advisor.  At least I think Varnedoe is still on faculty, at
least in an adjunct capacity.  At the IFA you also have to have a secondary
topic, and
you could also choose Rosenblum for 19th c. French art if you like.

I'd say just pick who you want to study with by reading their work, and then
go wherever they are.  Just make sure they won't be on sabbatical while
you're there:  this happened to a good friend of mine who chose his school
based on one scholar and then the scholar went on leave for 3 years!

Julia Moore
Indianapolis Art Center