Spin pseudogap

Key words Stripe Structure, Spin Density Wave, Pseudogap, Electron-phonon Interaction,... 

Abstract Existing data on 63Cu-nuclear spin relaxation reveal two independent relaxation processes the one that is temperature independent we link to incommensurate peaks seen by neutrons, while the "universal temperature dependent contribution coincides with 1/6371 (1/ ) for two-chain YBCO 124. We argue that this new result substitutes for a "pseudogap regime in a broad class of high-Tc cuprates and stems from the 1st order phase transition that starts well above the superconductivity Tc but becomes frustrated because of broken electroneutrality in the CuC>2 plane. 

A simple physical picture that is consistent with the above results is that above T one has coherent itinerant quasiparticle behavior over the entire Fermi surface, observed as an anomalous Fermi liquid. Below T one loses that coherent behavior for a portion of the Fermi surface near the antinodes the hot quasiparticles (those whose spin-fluctuation-induced interaction is strongest) found there enter the pseudogap state its formation is characterized by a transfer of quasiparticle spectral weight from low to high frequencies that produces the decrease in the uniform spin susceptibility below T. The remainder of the Fermi surface is largely unaffected. 

Key words Condensation energy, spin fluctuation mechanism of pairing, thermodynamic, underdoped region, pseudogap... 

As described above, there have been abundant results indicating the presence of some kind of energy gap which may be called either the pseudogap or the spin gap. Although the temperatures To and T below which the anomalies are noticed are not well defined, they both exhibit a similar dependence upon the carrier density, i.e., going up as the carrier density decreases into the underdoped regime, as summarized by Nakano et al. (1994). 

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