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

B L Ong; K Jayaraman; C Diao; T J Whitcher; A Jain; H Hung; M B H Breese; E S Tok; A Rusydi

doi:10.1038/s41467-022-31885-1

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

Nat Commun. 2022 Aug 8;13(1):4639. doi: 10.1038/s41467-022-31885-1.

Authors

B L Ong^#^{1

2}, K Jayaraman^#^{1

2}, C Diao², T J Whitcher^{1

2}, A Jain^{1

2}, H Hung¹, M B H Breese^{1

2}, E S Tok¹, A Rusydi^#^{3

4

5

6}

Affiliations

¹ Advanced Research Initiative for Correlated-Electron Systems (ARiCES), Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117551, Singapore.
² Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore.
³ Advanced Research Initiative for Correlated-Electron Systems (ARiCES), Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117551, Singapore. andrivo.rusydi@nus.edu.sg.
⁴ Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore. andrivo.rusydi@nus.edu.sg.
⁵ Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore. andrivo.rusydi@nus.edu.sg.
⁶ NUS Graduate School for Integrative Sciences and Engineering, Singapore, 117456, Singapore. andrivo.rusydi@nus.edu.sg.

^# Contributed equally.

Abstract

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_1.8Ba_0.2CuO₄/LaAlO₃(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 O2p-Cu3d-O2p is a triplet state yielding strong ferromagnetism. For out-of-ab-plane spin-polarization, while the spins of doped holes in both O2p-O2p and Cu3d-Cu3d are triplet states, the spin of doped holes in Cu3d-O2p 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.