SC state in the underdoped high-T_c cuprates as a quantum spin liquid. A microscopic theory

Abstract

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.