Anomalous Ferromagnetism of quasiparticle doped holes in cuprate heterostructures revealed using resonant soft X-ray magnetic scattering

• Published in: Nature communications 2022-08, Vol.13 (1), p.4639-4639, Article 4639
• Main Authors: Ong, B. L., Jayaraman, K., Diao, C., Whitcher, T. J., Jain, A., Hung, H., Breese, M. B. H., Tok, E. S., Rusydi, A.
• Format: Article
• Language: English
• Subjects: 639/301/119/2793; 639/301/119/544; 639/766/119/995; 639/766/119/997; Atomic energy levels; Circular dichroism; Copper; Cuprates; Dichroism; Elementary excitations; Ferrimagnetism; Ferromagnetism; Gold; Heterostructures; Humanities and Social Sciences; multidisciplinary; Polarization; Polarization (spin alignment); Quantum dots; Scattering; Science; Science (multidisciplinary); Soft x rays; Superconductors; Triplet state; Wave dispersion
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-31885-1

We report strong ferromagnetism of quasiparticle doped holes both within the ab- plane and along the c- axis of Cu-O planes in low-dimensional Au/ d- La 1.8 Ba 0.2 CuO 4 /LaAlO 3 (001) heterostructures ( d  = 4, 8 and 12 unit-cells) using resonant soft X-ray and magnetic scattering together with X-ray magnetic circular dichroism. Interestingly, ferromagnetism is stronger at a hole doped peak and at an upper Hubbard band of O with spin-polarization degree as high as 40%, revealing strong ferromagnetism of Mottness. For in- ab -plane spin-polarizations, the spin of doped holes in O2 p –Cu3 d –O2 p is a triplet state yielding strong ferromagnetism. For out-of- ab -plane spin-polarization, while the spins of doped holes in both O2 p –O2 p and Cu3 d –Cu3 d are triplet states, the spin of doped holes in Cu3 d –O2 p is a singlet state yielding ferrimagnetism. A ferromagnetic-(002) Bragg-peak of the doped holes is observed and enhanced as a function of d revealing strong ferromagnetism coupling between Cu-O layers along the c -axis. Long-range magnetic order of quasiparticle doped holes is important for understanding the physics of cuprate superconductors, albeit difficult to probe in experiments. Ong et al. observe ferromagnetism of quasiparticle doped holes in a cuprate heterostructure and discuss implications for cuprates in the ground state.