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 frailty of the $d$-wave superconducting state in underdoped cuprates. Using a combination of theoretical approaches we study a $t-J$ like model. We report an -- as yet unexplored -- instability that is brought about by an ``internal'' fluctuation (anti-symmetric mode) of the $d$-wave state. This new theoretical result helps in understanding recent ARPES and STM studies. We also suggest further experiments to uncover this physics.