Detection of a Cooper-pair density wave in Bi2Sr2CaCu2O8+x

Abstract

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. Such a state has been created in ultracold (6)Li gas but never observed directly in any superconductor. It is now widely hypothesized that the pseudogap phase of the copper oxide superconductors contains such a 'pair density wave' state. Here we report the use of nanometre-resolution scanned Josephson tunnelling microscopy 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 and at the Bi2Sr2CaCu2O8+x crystal supermodulation. Then, by using Fourier analysis of scanned Josephson tunnelling images, we discover the direct signature of a Cooper-pair density modulation at wavevectors QP ≈ (0.25, 0)2π/a0 and (0, 0.25)2π/a0 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 when a charge density wave with d-symmetry form factor and wavevector QC = QP coexists with a d-symmetry superconductor; it is also predicted by several contemporary microscopic theories for the pseudogap phase.

Dual gauge field theory of quantum liquid crystals in two dimensions

“…Recently evidence emerged that the superconductivity in static stripe systems may behave similar to the antiferromagnetism, with the phase of the order parameter reversing from stripe to stripe: the "pair density waves" [80,81]. One can imagine that similar "stripe fractionalization" topological orders may occur, now involving the superconducting order parameter [82].…”

Intertwined Order and Holography: The Case of Parity Breaking Pair Density Waves

“…A first example is the pattern of spontaneous electronic "orbital" currents encircling the plaquettes of the copper oxide planes [3][4][5], while there is definitive evidence for the breaking of parity [6]. Another example is the pair density wave (PDW): a superconducting state that does break translations in zero magnetic field, for which experimental evidence was reported in spinstriped 214 superconductors [7,8] and very recently in a charge ordered 2212 "BISCO" superconductor [9]. Departing from the established repertoire of condensed matter theories it appears to be quite difficult to explain the origin for the observed patterns of symmetry breaking in cuprates [10,11].…”

Quasiparticle Scattering off Defects and Possible Bound States in Charge-Ordered YBa2Cu3OyZhou1, Hirata2, Wu3 et al. 2017Phys. Rev. Lett.111331View full textAdd to dashboardCite

“…Finally, it should be mentioned that recent proposal of a pair-density-wave (PDW) state in the cuprates [4,[70][71][72] provides a tantalizing explanation of our data in terms of Andreev bound states at locations where the superconducting gap changes its sign. Zero-bias conductance peaks, a standard signature of bound states in STM, have been reported in La 1.88 Sr 0.12 CuO 4 and have actually been interpreted as evidence of PDW [73] (see also Refs.…”