Accessing topological magnonic excitations in non-equilibrium
Abstract
Topological bosonic excitations must, in contrast to their fermionic counterparts, appear at finite energies. This is a key challenge for magnons, as it prevents straightforward excitation and detection of topologically-protected magnonic edge states and their use in magnonic devices. However, magnonic systems can be easily driven out of equilibrium through spin-orbit torques, opening up new pathways for accessing topological magnonic excitations. This allows us to realize non-equilibrium and non-Hermitian topology in magnonic systems. In this talk I will discuss how this approach offers direct access to topological magnonic excitations. First, I will propose a general non-equilibrium strategy to access the topologically protected edge states in a magnon Chern insulator. In this non-equilibrium state, stabilized by spin-orbit torques, the topologically-protected chiral edge modes lie at zero frequency, while the bulk modes remain gapped. I will discuss the stability of this setup and the transport properties in the presence of disorder, and show how the presence of opposite frequency magnons can be detected. In a non-Hermitian topological magnon phase the edge modes can be externally controlled by applying a spin-orbit torque. I will demonstrate that this effect leads to a hybrid skin effect and the amplification or damping of the edge modes, which is robust against disorder. This opens up the possibility of realizing non-Hermitian topological phases in magnonic systems.
