Speaker
Description
We present a resonant inelastic and elastic X-ray scattering (RIXS/REXS) study of epitaxial YBa2Cu3O7/Nd1-x(Ca1-ySry)xMnO3 heterostructures (NYN). We show that the Copper charge density wave (Cu-CDW) order of the near optimally doped YBa2Cu3O7 layers can be strongly modified via the hole doping and tolerance factor of Nd1-x(Ca1-ySry)xMnO3, i.e. by changing x and y.
At x=0.35 we observe a quasi-2D Cu-CDW order with dx2-y2 orbital character that resembles the one that is commonly found in strongly underdoped bulk YBCO. The strength of the corresponding Bragg peak at Q||=0.3 r.l.u. gets strongly enhanced as the tolerance factor of the manganite layers[1] is decreased and its CE-type antiferromagnetic and charge/orbital ordered (COO) is reinforced[1].
Upon increasing the hole doping of the manganite layers to x=0.5, we observe a new kind of Cu-CDW order which has a much smaller wave vector of Q||=0.1 r.l.u., a larger correlation length of about 40nm, and a different orbital character, i.e. dz2 rather than dx2-y2, than the one commonly found in the bulk cuprates[2].
The origin of this new Cu-dz2 charge order is presently not understood, but seems to be rooted in the particular properties of the cuprate/manganite interface. The RIXS and additional x-ray absorption spectroscopy (XAS) data provide evidence for an important role of the orbital reconstruction of the Cu-ions at the interface with the manganite and a related transfer of electrons from the manganite to the cuprate. In particular, they show that the Cu-dz2 orbital of the interfacial Cu ions is strongly shifted up in energy and lies close to the Fermi-level such that it contains a significant part of the hole carriers, which usually mainly reside in the Cu-dx2-y2 orbital. This orbital reconstruction may well exhibit a lateral modulation along the interface that is linked with the anomalous dz2-type Cu-CDW order.
While further studies are required to fully understand the interfacial coupling mechanism(s), the possibility of tuning the Cu-CDW holds great prospects for studying its relationship with high temperature superconductors and hopefully, for future quantum devices.
References
1. E. Perret et al., Coupled Cu and Mn charge and orbital orders in YBa2Cu3O7/Nd0.65(Ca1-ySry)0.35MnO3 multilayers, Communications Physics 1, 45 (2018);
2. R. Gaina et al., Long-ranged Cu-based order with dz2 orbital character at a YBa2Cu3O7/ manganite interface. npj Quantum Materials 6, 12 (2021);
