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  Gaina, R.; Nicholson, C.W.; Rumo, M.; Sarkar, S.; Khmaladze, J.; Paris, E.; Tseng, Y.; Zhang, W.; Asmara, T.C.; McNally, D.; Piamonteze, C.; Weschke, E.; Schmitt, T.; Monney, C.; Bernhard, C.: Long-ranged Cu-based order with d_z² orbital character at a YBa₂Cu₃O₇/manganite interface. npj Quantum Materials 6 (2021), p. 12/1-8

10.1038/s41535-021-00311-y
Open Access Version

Abstract:
The interplay of nearly degenerate orders in quantum materials can lead to a myriad of emergent phases. A prominent case is that of the high-Tc cuprates for which the relationship between superconductivity and a short-ranged, incommensurate charge density wave in the CuO2 planes involving the dx2−y2 orbitals (Cu-CDW) is a subject of great current interest. Strong modifications of the strength and coherence of this Cu-CDW have been achieved by applying large magnetic fields, uniaxial pressure, or via the interfacial coupling in cuprate/manganite multilayers. However, such modifications do not alter the dominant orbital character. Here we investigate cuprate/manganite multilayers with resonant inelastic X-ray scattering (RIXS) and show that a new kind of Cu-based density wave order can be induced that has not been previously observed in the cuprates. This order has an unusually small in-plane wave vector in the range of Q|| < 0.1 reciprocal lattice units (r.l.u.), a large correlation length of about 40 nm, and a predominant dz2 orbital character, instead of the typical dx2−y2 one. Its appearance is determined by the hole doping of the manganite which is a key parameter controlling the interfacial charge transfer and orbital reconstruction. We anticipate that the observation of a previously unknown type of density wave order at the YBCO interface will allow for fresh perspectives on the enigmatic relation between superconductivity and charge order (CO) in the cuprates.