Encirclement of an exceptional point and eigenvalue switch in non-Hermitian coupled spintronic nano-oscillators

Exceptional points (EPs) are known for their unique topological behaviors, including eigenvalue and eigenvector switching and high sensitivity to parameter changes. While EPs are usually studied in parity-time (PT) symmetric systems, we investigate the presence of EPs in the more general case of purely non-Hermitian systems. Using coupled spintronic auto-oscillators with uncompensated gain/loss, we explore the parameter space of the coupled system by fine-tuning the spin-transfer torque effect and its relative phase. Using this approach, we reveal and investigate the generalized presence of EPs. These tuning mechanisms provide direct control over the coupling nature, from conservative to dissipative. Moreover, we demonstrate the topological nature of the EP by dynamical encircling it in the phase-current parameter space, resulting in a switch of the eigenvalues. Our study introduces a new and versatile approach for exploring non-Hermitian physics in spintronic systems at room temperature.