Abstract

Single crystalline thin film heterostructures made of optimally doped YBa2Cu3O7 and charge-orbital-ordered insulating Nd1-x(Ca1-ySry)xMnO3(NCSMO) exhibit a plethora of interesting and unusual physical properties. Using Resonant elastic and inelastic x-ray scattering (REXS/RIXS) in conjunction with x-ray linear and magnetic dichroism (XLD/XMCD), we measured the systematic modification of orbital characteristics, magnonic properties and charge density wave (CDW) in YBCO , as a function of the hole doping and tolerance factor of the neighboring NCSMO layers.

For x=0.35, we observe a Cu-CDW order with the usual 𝑑𝑥2−𝑦2 orbital character at Q||=0.3 r.l.u, which gets strongly enhanced as the tolerance factor of the manganite layers is decreased or when a strong magnetic field is applied [1]. On the other hand, for x=0.5 and y=0.25, we observe a completely new kind of Cu-order which has a small wave vector of Q||=0.1 r.l.u., a very large correlation length of about 40nm and a completely different 𝑑𝑧2 orbital character [2].

Further, for samples with x=0.35 and y=0.3, we find an altermagnetic order that coexist with the above-mentioned magnetically tunable charge density wave at the interface [3]. Cu-RIXS spectra and its polarization analysis indicate the presence of two separate Cu-magnon modes corresponding to the bulk and the interface of YBCO . While the bulk mode disperses as usual as antiferromagnetic spin-fluctuations in the 123-cuprate family, the weakly dispersing interfacial mode exhibits a decreasing weight with increasing momentum transfer. This anomalous magnon-behavior can be explained by a linear spin wave theory that takes in to account a 2-D checkerboard-type orbital pattern of 𝑑𝑥2−𝑦2 and 𝑑3𝑧2−𝑟2 (as suggested from XLD ), coupled with a spin-order leading to an altermagnetic property at the interface.

Finally, in similar multilayers, we observe below ~120K a spontaneous voltage (SpV) signal that can be used for driving a persistent current across an external circuit [4]. This SpV signal also exhibits an intriguing magnetic field dependence with an overall strong suppression towards large magnetic fields and hysteretic, jump-like changes at intermediate values of magnetic field. The mechanism underlying the SpV involves ambient electronic noise rectification due to a ratchet-type electronic potential originating from a competing coexistence of a nonpolar ferromagnetic (FM) minority phase and a charge/orbital ordered (COO) majority phase with polar moments and charged domain walls.

References:[ 1] R. Gaina et al., Phys. Rev. B 104 , 174513 (2021). [2] R. Gaina et al. npj Quantum Mater. 6, 12 (2021). [3] S. Sarkar et al., PNAS Nexus 3 (2024), pgae100 [4] M. Soulier et al., Spontaneous voltage and persistent electric current from rectification of electronic noise in cuprate/manganite heterostructures, under review