Selective interlayer ferromagnetic coupling between the Cu spins in YBa2Cu3O7-x grown on top of La0.7Ca0.3MnO3.

S W Huang,Horng-Tay Jeng,J.-Y Lin,J M Lee,R W Schoenlein,V T Tra,M C Langner,Y.-D Chuang,S Roy,L Andrew Wray,Y H Chu,J M Chen

doi:10.1038/srep16690

Abstract

Studies to date on ferromagnet/d-wave superconductor heterostructures focus mainly on the effects at or near the interfaces while the response of bulk properties to heterostructuring is overlooked. Here we use resonant soft x-ray scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between the in-plane Cu spins in YBa2Cu3O7−x (YBCO) superconductor when it is grown on top of ferromagnetic La0.7Ca0.3MnO3 (LCMO) manganite layer. This coupling, present in both normal and superconducting states of YBCO, is sensitive to the interfacial termination such that it is only observed in bilayers with MnO2 but not with La0.7Ca0.3O interfacial termination. Such contrasting behaviors, we propose, are due to distinct energetic of CuO chain and CuO2 plane at the La0.7Ca0.3O and MnO2 terminated interfaces respectively, therefore influencing the transfer of spin-polarized electrons from manganite to cuprate differently. Our findings suggest that the superconducting/ferromagnetic bilayers with proper interfacial engineering can be good candidates for searching the theorized Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the competing quantum orders in highly correlated electron systems.

Highlights

With advanced thin-film growth technology[6,7,8,9,10], heterostructures made out of superconducting cuprates and ferromagnetic manganites can serve as an ideal platform for such studies
Due to very small mismatch between the in-plane lattice constants of YBCO and LCMO, epitaxial growth of YBCO/LCMO bilayers with atomically smooth interfaces can be achieved
We have identified a novel inter-unit-cell ferromagnetic coupling between the in-plane Cu spins in YBCO based on the clear φ and temperature dependence of YBCO (001) Bragg peak intensity recorded at Cu2+ resonance energy

Summary

Introduction

With advanced thin-film growth technology[6,7,8,9,10], heterostructures made out of superconducting cuprates and ferromagnetic manganites can serve as an ideal platform for such studies. Measurements on YBa2Cu3O7−x/La0.7Ca0.3MnO3 (YBCO/LCMO) heterostructures have revealed an induced ferromagnetic Cu spin moment in the interfacial CuO2 plane that couples antiferromagnetically to the underlying Mn spin moment[6] Interesting phenomena such as ferromagnetism/superconductivity proximity[11,12] and inverse proximity effect[13], transfer of spin-polarized electrons from manganite to cuprate[14], and the electronic orbital reconstruction at the interface[7] were observed and proposed to account for the suppression of both ferromagnetism and d-wave superconductivity upon forming such heterostructures (Fig. 1(a)). We use bulk-sensitive resonant soft x-ray scattering spectroscopy (RSXS) and first principles calculations to show that beyond the interface, a novel ferromagnetic order can be established within the YBCO layer possibly even in the superconducting state. This c-axis ferromagnetic coupling between the in-plane Cu spins is subtle and can be effectively controlled by the interfacial termination

Methods

Results

Conclusion