Coupled Cu and Mn charge and orbital orders in cuprate/manganite multilayers

The observation of a charge density wave (CDW) phase involving Cu $d_{x2-y2}$ orbitals in underdoped high $T_c$ cuprate superconductors has triggered an intense research effort for exploring its relation to superconductivity. In this framework, heterostructures of cuprate layers together with manganite layers offer the appealing possibility of manipulating the CDW vs superconductivity competition. This is effectively done by tuning the chemical composition of the manganite layer to play with is complex phase diagram.

Here we study the proximity effect at the interface of Nd$_x$(Ca$_{1-y}$Sr$_y$)$_{1-x}$MnO$_3$ (NCSMO) and YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) with resonant inelastic x-ray scattering (RIXS) at the Cu L-edge. In this talk, I will present two cases. First, for an heterostructure with x=0.35 and small values of y~0.3, the manganite layer is in an CE-type antiferromagnetic phase with a charge and orbital order (Mn-COO) [1]. Using RIXS, we show that the magnitude of the CDW in the cuprate layer at Q=0.33 reciprocal lattice units (rlu) can be varied by adjusting the strength of the Mn-COO in the manganite layer via the substitution y. Furthermore, we observe a strong reconstruction of the crystal field excitations at the Cu sites near the interface, which we can probe selectively thanks to a specific resonance in the x-ray absorption [2].

Then, I will present the case of an heterostructure with x=0.5 and y=0.25, with a particularly strong and long-range ordering. To our surprise, for these samples, we do not observe any CDW at Q=0.33 rlu in the cuprate layer, but we discover a new order with Q=0.1 rlu at the interface with the manganite layer. Furthermore, by doing a detailed x-ray polarization study of the related superstructure signal in RIXS, we conclude that this order is not involving Cu dx2-y2 orbitals, but rather Cu d3z2-r2 orbitals [3].
From our study, we conclude that NCSMO/YBCO heterostructures allow manipulating the CDW phase in the Cu layer. The manganite layer plays this role not only by the presence of magnetism, but also by offering an ordered template with the different charge and orbital ordered phases setting in as a function of substitution y.

[1] Tokura, Y., Rep. Prog. Phys. 69, 797 (2006).
[2] Perret, E., Monney, C. Johnston, S., Khmaladze, J., Lyzwa, F., Gaina, R., Dantz, M., Pelliciari, P., Piamonteze, C., Mallett, B.P.P., Minola, M., Keimer, B., Schmitt, T., Bernhard, C., Communications Physics 1, 45 (2018).
[3] 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. and Bernhard, C., npj Quantum Materials 6, 12 (2021).