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Simultaneous Transitions in Cuprate Momentum-Space Topology and Electronic Symmetry Breaking

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Science  09 May 2014:
Vol. 344, Issue 6184, pp. 612-616
DOI: 10.1126/science.1248783

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Under the Dome

The superconducting transition temperature Tc of copper oxides has a dome-shaped dependence on chemical doping. Whether there is a quantum critical point (QCP) beneath the dome, and whether it is related to the enigmatic pseudogap, has been heavily debated. Two papers address this question in two different families of Bi-based cuprates. In (Bi,Pb)2(Sr,La)2CuO6+δ, He et al. (p. 608) found that the Fermi surface (FS) undergoes a topological change as doping is increased, which points to the existence of a QCP at a doping close to the maximum in Tc, seemingly uncorrelated with the pseudogap. Fujita et al. (p. 612) studied a range of dopings in Bi2Sr2CaCu2O8+δ to find an FS reconstruction simultaneous with the disappearance of both rotational and translational symmetry breaking, the latter of which has been associated with the pseudogap. These findings point to a concealed QCP.

Abstract

The existence of electronic symmetry breaking in the underdoped cuprates and its disappearance with increased hole density p are now widely reported. However, the relation between this transition and the momentum-space Embedded Image electronic structure underpinning the superconductivity has not yet been established. Here, we visualize the Embedded Image (intra–unit-cell) and Embedded Image (density-wave) broken-symmetry states, simultaneously with the coherent Embedded Image topology, for Bi2Sr2CaCu2O8+δ samples spanning the phase diagram 0.06 ≤ p ≤ 0.23. We show that the electronic symmetry-breaking tendencies weaken with increasing p and disappear close to a critical doping pc = 0.19. Concomitantly, the coherent Embedded Image topology undergoes an abrupt transition, from arcs to closed contours, at the same pc. These data reveal that the Embedded Image topology transformation in cuprates is linked intimately with the disappearance of the electronic symmetry breaking at a concealed critical point.

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