Chimeras and complex cluster states in arrays of spin-torque oscillators

Abstract

We consider synchronization properties of arrays of spin-torque nano-oscillators coupled via an RC load. We show that while the fully synchronized state of identical oscillators may be locally stable in some parameter range, this synchrony is not globally attracting. Instead, regimes of different levels of compositional complexity are observed. These include chimera states (a part of the array forms a cluster while other units are desynchronized), clustered chimeras (several clusters plus desynchronized oscillators), cluster state (all oscillators form several clusters), and partial synchronization (no clusters but a nonvanishing mean field). Dynamically, these states are also complex, demonstrating irregular and close to quasiperiodic modulation. Remarkably, when heterogeneity of spin-torque oscillators is taken into account, dynamical complexity even increases: close to the onset of a macroscopic mean field, the dynamics of this field is rather irregular.

Chimeras on a social-type network

“…In spatially extended systems chimera appears as a localized pattern of asynchrony [2][3][4][5][6][7][8][9][10][11][12]. In globally coupled populations chimeras are also possible: they emerge not as spatial patterns, rather a group of asynchronous oscillators "detaches" from the synchronous cluster [13][14][15][16][17].…”

Analyzing synchronized clusters in neuron networks

“…The proposed approach can be applied to other neuron-like multi-layer networks of oscillators, provided that they can be described through the proposed formalism. For instance, cluster synchronization in arrays of spin-torque oscillators 48 or semiconductor laser arrays 49 could be analyzed through the proposed method.…”

Synchrony breakdown and noise-induced oscillation death in ensembles of serially connected spin-torque oscillators

“…Numerical experiments with the STO ensembles beyond the threshold values of constant current I in different circuit configurations disclose, mostly, complicated dynamical states with various degrees of asynchrony [20,24]; in Fig. 6 we exemplify a few of them by projecting all magnetization vectors onto the same spherical surface.…”