Orbital Symmetries of Charge Density Wave Order in YBa2Cu3O6+x

Abstract

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.Comment: 17 pages, 4 figures + supplementary informatio