Nonlinear dynamics and imaging of current density and electric field bifurcations caused by electronic instabilities

In 1963 Ridley postulated that, under appropriate biasing conditions, a system that exhibits either a current-controlled or a voltage-controlled negative differential resistance will bifurcate, via entropy-production-maximization, to form regions with different current-densities or electric-fields, respectively. The ensuing widespread discussions in the non-equilibrium statistical mechanics community, however, failed to agree on specific mechanisms causing such bifurcations. Using thermal and chemical spectro-microscopy, my group directly imaged current-density- and electric-field-bifurcations in transition metal oxides that are being used to implement threshold resistance switching in memristors and enable new types of neuro-mimetic devices. We found that nonlinear dynamical circuit theory and the principle of local activity successfully predict both chaotic dynamical behavior and current-density- and electric-field-bifurcations, as well as provides a mechanism for why the bifurcations occur. We determined that upon bifurcations, internal enthalpy in the device reduces despite unchanged power input and heat output, thus suggesting an important thermodynamic constraint required to model nonlinear electronic devices. Our results explain the electroforming process that initiates nonvolatile switching in metal oxides and has significant implications for properly modeling any semiconductor device, since bifurcation can occur for many types of activated processes.