Composite antiferromagnetic and orbital order with altermagnetic properties at a cuprate/manganite interface

Abstract

Heterostructures from complex oxides allow one to combine various electronic and magnetic orders as to induce new quantum states. A prominent example is the coupling between superconducting and magnetic orders in multilayers from high-$T_c$ cuprates and manganites. A key role is played here by the interfacial CuO₂ layer whose distinct properties remain to be fully understood. Here, we study with resonant inelastic X-ray scattering the magnon excitations of this interfacial CuO₂ layer. In particular, we show that the underlying antiferromagnetic exchange interaction at the interface is strongly suppressed to $J\approx 70$ meV, when compared with $J\approx 130$ meV for the CuO₂ layers away from the interface. Moreover, we observe an anomalous momentum dependence of the intensity of the interfacial magnon mode and show that it suggests that the antiferromagnetic order is accompanied by a particular kind of orbital order that yields a so-called altermagnetic state. Such a 2D altermagnet has recently been predicted to enable new spintronic applications and superconducting proximity effects.

Keywords: RIXS; altermagnetism; cuprates; magnons; superconductivity.