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Hamidian, M. H.,Edkins, S. D.,Joo, Sang Hyun,Kostin, A.,Eisaki, H.,Uchida, S.,Lawler, M. J.,Kim, E.-A.,Mackenzie, A. P.,Fujita, K.,Lee, Jinho,Davis, J. C. Sé,amus Nature Publishing Group, a division of Macmillan P 2016 Nature Vol.532 No.7599
<P>The quantum condensate of Cooper pairs forming a superconductor was originally conceived as being translationally invariant. In theory, however, pairs can exist with finite momentum Q, thus generating a state with a spatially modulated Cooper-pair density(1,2). Such a state has been created in ultracold Li-6 gas(3) but never observed directly in any superconductor. It is now widely hypothesized that the pseudogap phase(4) of the copper oxide superconductors contains such a 'pair density wave' state(5-21). Here we report the use of nanometre-resolution scanned Josephson tunnelling microscopy(22-24) to image Cooper pair tunnelling from a d-wave superconducting microscope tip to the condensate of the superconductor Bi2Sr2CaCu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms(25) and at the Bi2Sr2CaCu2O8+x crystal supermodulation(26). Then, by using Fourier analysis of scanned Josephson tunnelling images, we discover the direct signature of a Cooper-pair density modulation at wavevectors Q(P) approximate to (0.25, 0)2 pi/a(0) and (0, 0.25)2 pi/a(0) in Bi2Sr2CaCu2O8+x. The amplitude of these modulations is about five per cent of the background condensate density and their form factor exhibits primarily s or s' symmetry. This phenomenology is consistent with Ginzburg-Landau theory(5,13,14) when a charge density wave(5,27) with d-symmetry form factor(28-30) and wavevector Q(C) = Q(P) coexists with a d-symmetry superconductor; it is also predicted by several contemporary microscopic theories for the pseudogap phase(18-21).</P>
Simultaneous Transitions in Cuprate Momentum-Space Topology and Electronic Symmetry Breaking
Fujita, K.,Kim, Chung Koo,Lee, Inhee,Lee, Jinho,Hamidian, M. H.,Firmo, I. A.,Mukhopadhyay, S.,Eisaki, H.,Uchida, S.,Lawler, M. J.,Kim, E.-A.,Davis, J. C. American Association for the Advancement of Scienc 2014 Science Vol.344 No.6184
<P><B>Under the Dome</B></P><P>The superconducting transition temperature <I>T<SUB>c</SUB></I> 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)<SUB>2</SUB>(Sr,La)<SUB>2</SUB>CuO<SUB>6+δ</SUB>, <B>He <I>et al.</I></B> (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 <I>T<SUB>c</SUB></I>, seemingly uncorrelated with the pseudogap. <B>Fujita <I>et al.</I></B> (p. 612) studied a range of dopings in Bi<SUB>2</SUB>Sr<SUB>2</SUB>CaCu<SUB>2</SUB>O<SUB>8+δ</SUB> 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.</P>