We studied how the electronic, superconducting, and magnetic properties of YBa 2 Cu 3 O 7 / Nd 1−x (Ca 1−y Sr y ) x MnO 3 multilayers depend on the tolerance factor and the hole doping of the manganite. In particular, we investigated the granular superconducting state and the related magnetic-field-driven insulator-to-superconductor transition that was previously discovered in corresponding multilayers with Pr 0.5 La 0.2 Ca 0.3 MnO 3 [B. P. P. Mallett et al., Phys. Rev. B 94, 180503(R) ( 2016)]. We found that this granular superconducting state occurs only when the manganite layer is in a charge/orbital ordered and CE-type antiferromagnetic state (Mn-CO/OO). The coupling mechanism underlying this intriguing proximity effect seems to involve the domain boundaries of the Mn-CO/OO and/or the charge disordered regions of the manganite layer that become more numerous as the hole doping is reduced below x = 0.5.

Terahertz vortex beams with different superposition of the orbital angular momentum l ¼ AE1, AE2, AE3, and AE4 and spin angular momentum σ ¼ AE1 were used to study antiferromagnetic (AFM) resonances in TbFe 3 ðBO 3 Þ 4 and Ni 3 TeO 6 single crystals. In both materials we observed a strong vortex beam dichroism for the AFM resonances that are split in external magnetic field. The magnitude of the vortex dichroism is comparable to that for conventional circular dichroism due to σ. The selection rules at the AFM resonances are governed by the total angular momentum of the vortex beam: j ¼ σ þ l. In particular, for l ¼ AE2, AE3, and AE4 the sign of l is shown to dominate over that for conventional circular polarization σ.

For a YBa 2 Cu 3 O 7 /Nd 0.65 (Ca 0.7 Sr 0.3 ) 0.35 MnO 3 (YBCO/NCSMO) superlattice, we studied with resonant elastic x-ray scattering (REXS) at the Cu L 3 edge how the copper sublattice charge density wave (Cu-CDW) order in YBCO is affected by a large magnetic field up to 6.9 T that weakens the CE-type antiferromagnetic (AF) and the charge/orbital (Mn-CO) orders of the manganite in favor of a ferromagnetic state. While a field of only 2 T induces a strong ferromagnetic moment in the manganite, we find that the Bragg peak of the Cu-CDW hardly changes up to 6 T. Moreover, as the magnetic field is further increased to 6.9 T, the Cu-CDW Bragg peak gets suddenly enhanced and broadened, whereas the ferromagnetic moment of the manganite is already saturated. The observed uncorrelated magnetic field dependence of the charge orders in the cuprate and manganite layers suggests that these orders are not directly coupled across the interface. We rather interpret our data in terms of an indirect coupling via the domain boundaries of the Mn-CO and the related disorder and lattice strain. This interpretation is supported by additional studies of the magnetoelectric response, which provide evidence for a crossover in the dynamics of the Mn-CO in the range between 6 and 7 T, from a low-field state with pinned domains to a high-field state with more mobile and flexible domain boundaries. We attribute the concomitant enhancement and broadening of the Cu-CDW Bragg peak to this crossover.