Competing gaps scenario for underdoped cuprates

The normal state properties are definitely more exotic than the superconducting properties of the engimatic quasi-2D d-wave cuprate superconductors. Under special inspection is the psudogap state, which is signalled with a loss in quasi-particle spectral weight above a typical temperature T*, which is much higher than Tc, the SC critical temperature. A basic question concerns the nature of this gap opening. One idea precasts that the pseudogap senses the preformed cooper pairs, which will condense into a coherent superfluid at Tc. Another idea relates this gap to a different order, which might compete with the SC order. Up to now, evidences regarding these two ideas are elusive. This terrific work [Nature Physics, 7: 21–25 (2011) doi:10.1038/nphys1851] comes to give a real boost. They study Bi2212 with various dopings. They focus on the temperature dependence of the weight loss associated with the antinodal point in the 1BZ. As the sample is cooled across T*, a linear tempeature dependence was spotted around T*, but a very fast deviation sets in at lower temperatures, T**>Tc. This deviation motivates the authors to conceive a two-gap scenario: the proper pseudogap opens at T*, but the cooper pair forms at T**, and SC coherence comes at Tc. According to this proposition, the pseudogap has a separate origin that should be concerned with a different order. They are able to find out a remarkably accurate scaling behaviors regarding the dependence of the cooper paring spectral weight loss on the T**. This scaling law holds for all samples they prepared. Read this paper !! Very inspiring !!