Critical role of the sign structure in the doped Mott insulator: Superconductivity vs. Fermi liquid
Abstract
Mechanism of superconductivity (SC) in a purely interacting electron system has been one of the most challenging issues in condensed matter physics. In the BCS theory, the Landau's Fermi liquid is a normal state against which an SC instability occurs once an additional pairing force is added. We show that in the doped Mott insulator an intrinsic SC ground state (specifically a Luther-Emery state in a finite-doping two-leg t-J ladder) can be directly turned into a Fermi-gas-like state by merely switching off the hidden statistical sign structure via two schemes. It points to a new pairing paradigm, %beyond the resonating-valence-bond scheme, which is an "Amperean-like pairing" with a "stringlike" pairing force as shown by an adiabatic continuity to a strong anisotropic limit of the model.