Probing phase coupling between two spin-torque nano-oscillators with   external source
  Phase coupling between auto-oscillators is central for achieving coherent responses such as synchronization. Here we present an experimental approach to probe it in the case of two dipolarly coupled spin-torque vortex nano-oscillators using an external microwave field. By phase-locking one oscillator to the microwave field, we observe frequency pulling on the second oscillator. From coupled Thiele equations we show analytically that this frequency pulling results from concerted actions of dipolar and microwave couplings. The analysis allows us to determine the amplitude of dipolar coupling and the phase lag of each oscillator, yielding important information for the implementation of large oscillator networks. 
Yi Li, Xavier de Milly, Flavio Abreu Araujo, Olivier Klein, Vincent   Cros, Julie Grollier and Gr\'egoire de Loubens
cond-mat.mes-hall