Questioning the cuprate paradigm: Absence of superfluid density loss in several overdoped cuprates II

Abstract

For over 30 years it has been known that overdoped cuprate superconductors display a rapid fall in superfluid density (SFD) with increasing doping p along with the decline in Tc. This unconventional behavior suggests a depletion of the condensate either by increasing pairbreaking or the growth of a second nonpairing channel. One widely accepted suggestion is that the entire Tc(p) phase curve is governed by phase fluctuations arising from an already low SFD. More recently, it was proposed that the condensate arises in an incoherent charge channel that progressively gives way with overdoping to a second, coherent nonpairing channel. Here, we examine the electronic specific heat, and its field dependence, of a number of canonical cuprates and find that there is no apparent loss of SFD with overdoping. The SFD per CuO2 plaquette is found to rise progressively from p on the underdoped side towards (1+p) on the overdoped side, much the same as the Hall number. This would imply that all available carriers contribute to the condensate. If so, this could be the underlying intrinsic behavior for all generic cuprates. Our specific heat samples include (Y,Ca)Ba2Cu3O7−δ, YBa2Cu4O8, Bi2Sr2CaCu2O8+δ, La2−xSrxCuO4, Tl0.5Pb0.5Sr2Ca1−xYxCu2O7, and Tl2Ba2CuO6, with the latter being the only clear exception. The question arises as to why. Notably, any nongeneric behavior seems to be confined to the region beyond critical doping where the pseudogap closes.

Source-reported materials — not catalogue approval

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