Orbital torques and orbital pumping in two-dimensional rare-earth dichalcogenides

TL;DR

This paper explores the potential of 2D rare-earth dichalcogenides with Eu ions for spin-orbit torque applications, revealing significant orbital responses and the ability to generate in-plane orbital currents, advancing orbitronics.

Contribution

It demonstrates that Eu-based 2D dichalcogenides exhibit strong orbital torques driven by orbital responses, highlighting their promise for orbitronics and in-plane orbital current generation.

Findings

Significant spin-orbit torques originate from orbital responses in Eu 4f-electrons.

Orbital torques can drive strong in-plane orbital angular momentum currents.

Eu-based 2D materials are promising for orbitronics applications.

Abstract

The design of spin-orbit torque properties in two-dimensional (2D) materials presents one of the challenges of modern spintronics. In this context, 2D layers involving rare-earth ions $-$ which give rise to robust magnetism, exhibit pronounced orbital polarization of the states, and carry strong spin-orbit interaction $-$ hold particular promise. Here, we investigate ferromagnetic Janus H-phase monolayers of 4$f$-Eu rare-earth dichalcogenides EuSP, EuSSe, and EuSCl using first-principles calculations. We demonstrate that all compounds exhibit significant spin-orbit torques which originate predominantly in the colossal current-induced orbital response on the Eu $f$-electrons. Moreover, we demonstrate that the corresponding orbital torques can be used to drive strong in-plane currents of orbital angular momentum with non-trivial direction of orbital polarization. Our findings promote $f$-orbital-based 2D materials as a promising platform for in-plane orbital pumping and spin-orbit torque applications, and motivate further research on educated design of orbital properties for orbitronics with 2D materials.