Search

Charge density wave (CDW) order has been shown to compete and coexist with superconductivity in underdoped cuprates. Theoretical proposals for the CDW order include an unconventional $d$-symmetry form factor CDW, evidence for which has emerged from measurements, including resonant soft x-ray scattering (RSXS) in YBa$_2$Cu$_3$O$_{6+x}$ (YBCO). Here, we revisit RSXS measurements of the CDW symmetry in YBCO, using a variation in the measurement geometry to provide enhanced sensitivity to orbital symmetry. We show that the $(0\ 0.31\ L)$ CDW peak measured at the Cu $L$ edge is dominated by an $s$ form factor rather than a $d$ form factor as was reported previously. In addition, by measuring both $(0.31\ 0\ L)$ and $(0\ 0.31\ L)$ peaks, we identify a pronounced difference in the orbital symmetry of the CDW order along the $a$ and $b$ axes, with the CDW along the $a$ axis exhibiting orbital order in addition to charge order., 17 pages, 4 figures + supplementary information

Picking out the elusive stripes Copper-oxide superconductors have periodic modulations of charge density. Typically, the modulation is not the same for the whole crystal, but breaks up into small nanosized domains. Bulk experiments show that the density is modulated along both axes in the copper-oxide plane, but it is not clear whether this is true only on the scale of the whole crystal or also locally, for each domain. Comin et al. analyzed the charge order in the compound YBa 2 Cu 3 O 6+y , using resonant x-ray scattering, and found that it was consistent with a local unidirectional, so-called stripy, ordering. Science , this issue p. 1335

Finding order in exotic superconductors Physicists can coax some copper-oxide compounds into becoming superconducting by chemically adding extra charge carriers: holes or electrons. Concentrating on hole-doped materials, researchers have found a host of different phases in the neighborhood of or co-existing with superconductivity. One such phase is a modulation in charge density [a charge density wave (CDW)] that appears to be ubiquitous in hole-doped families. Da Silva Neto et al. now show that a similar phase exists in the electron-doped material Nd 2- x Ce x CuO 4 . As they cooled the material, the authors first detected the CDW at temperatures considerably higher than in the hole-doped copper-oxides. Science , this issue p. 282

The understanding of the origin of superconductivity in cuprates has been hindered by the apparent diversity of intertwining electronic orders in these materials. We combined resonant x-ray scattering (REXS), scanning-tunneling microscopy (STM), and angle-resolved photoemission spectroscopy (ARPES) to observe a charge order that appears consistently in surface and bulk, and in momentum and real space within one cuprate family, Bi 2 Sr 2 − x La x CuO 6 + δ . The observed wave vectors rule out simple antinodal nesting in the single-particle limit but match well with a phenomenological model of a many-body instability of the Fermi arcs. Combined with earlier observations of electronic order in other cuprate families, these findings suggest the existence of a generic charge-ordered state in underdoped cuprates and uncover its intimate connection to the pseudogap regime.