Ferromagnetic order beyond the superconducting dome in a cuprate superconductor*

The cuprate high-Tc superconductors have been the subject of intense study for more than 30 years with no consensus yet on the underlying
mechanism of the superconductivity (SC). Conventional wisdom dictates that the mysterious and extraordinary properties of the cuprates arise from doping a strongly correlated antiferromagnetic insulator. Although the normal state of the SC cuprates is a strange metal, the highly overdoped cuprates−those beyond the dome of superconductivity–are considered to be conventional Fermi liquid metals. In this talk, I will report experiments that show the emergence of itinerant ferromagnetic order (FM) below 4K for doping beyond the SC dome in the electron-doped cuprate La_2−xCe_xCuO₄ (LCCO). The existence of this FM order is evidenced by negative and anisotropic magnetoresistance, hysteretic magnetization and the polar Kerr effect, all of which are standard signatures of itinerant FM in metals (1). This surprising new result suggests that the overdoped cuprates are also influenced by electron correlations and the physics is much richer
than that of a conventional Fermi liquid metal.

1) T. Sarkar et al. arXiv:1902.11235 (2019)