Fermi liquid behavior and spin-charge separation in underdoped cuprates

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The Gaussian fluctuations in slave-boson mean-field theory of t-J model is analyzed in this paper in the low-doping regime where the superconducting to normal (pseudo-gap phase) transition is driven by vanishing of bose-condensation amplitude. By eliminating the boson and constraint fields exactly in the linear response regime we show that the Gaussian theory describes a Fermi liquid superconductor where the superconducting to normal transition is actually a spin-charge separation transition characterized by a change of Landau parameter from F₁>-1 in the superconducting phase to F₁=-1 in the pseudo-gap phase. Consequences of this proposal are discussed.