Pseudogap and competing states in underdoped cuprates

I shall argue that the high T-c problem is the problem of doping into a Mott insulator. Furthermore, the well documented pseudo-gap phenomenon in underdoped cuprates holds the key to understanding this physics. Phase fluctuation alone cannot explain this phenomenon, but there is a clear need to identify a competing state which lives in the vortex core. The staggered flux state is a good candidate for the competing state and experimental tests of these ideas will be discussed. (C) 2004 Published by Elsevier B.V.