Orbital symmetries of charge density wave order in YBa<sub>2</sub>Cu<sub>3</sub>O<sub>6+<i>x</i></sub>.

McMahon, Christopher; Achkar, A J; da Silva Neto, E H; Djianto, I; Menard, J; He, F; Sutarto, R; Comin, R et al. · Sci Adv · 2020

basic_science · Level V

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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 <i>d</i>-symmetry form factor CDW, evidence for which has emerged from measurements, including resonant soft x-ray scattering (RSXS) in YBa<sub>2</sub>Cu<sub>3</sub>O<sub>6+<i>x</i></sub> (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 <i>L</i>) CDW peak measured at the Cu <i>L</i> edge is dominated by an <i>s</i> form factor rather than a <i>d</i> form factor as was reported previously. In addition, by measuring both (0.31 0 <i>L</i>) and (0 0.31 <i>L</i>) peaks, we identify a pronounced difference in the orbital symmetry of the CDW order along the <i>a</i> and <i>b</i> axes, with the CDW along the <i>a</i> axis exhibiting orbital order in addition to charge order.