Crucial role of internal collective modes in underdoped cuprates

The enigmatic cuprate superconductors have attracted resurgent interest with several recent reports and discussions of competing orders in the underdoped side. Motivated by this, here we address the natural question of fragility of the d-wave superconducting state in underdoped cuprates. Using a combination of theoretical approaches we study $t\text{-}J$–like models, and discover an —as yet unexplored— instability that is brought about by an "internal" (anti-symmetric mode) fluctuation of the d-wave state. This new theoretical result is in good agreement with recent STM and ARPES studies of cuprates. We also suggest experimental directions to uncover this physics. (letter)