  We have discovered a new example of quantum spin liquid which is a
superconducting (SC) phase in 2D electron system close to electronic
topological transition. As a quantum spin liquid in low dimensional localized
spin systems it is characterized by a resonance spin mode and a well separated
two-particle continuum. Application of the theory to the high-T_c cuprates
allows to shed light on many observed in the underdoped regime features such as
the so called 40 meV resonance peak, incommensurability at lower \omega, spin
gap etc.
