The fourth circuit element

Abstract

Arising from: D. B. Strukov, G. S. Snider, D. R. Stewart & R. S. Williams Nature 453, 80–83 (2008)10.1038/nature06932

In 1971, Chua suggested¹ that there should in principle exist a circuit element linking electrical charge, q, and magnetic flux, ϕ. Strukov et al.² claim recently to have found such a link. However, here I point out that Chua’s suggestion was in fact preceded by experimental evidence^3,4,5 for magneto-electric effects whereby magnetic and electrical signals are interconverted. When the stimulus is magnetic and the response is electrical, the linear magneto-electric coupling constant⁵, α, is typically reported as dP/dH, where P represents the electrical polarization and H represents the applied magnetic field. The coupling constant could equally be presented as dq/dϕ if divided by the permeability of free space.

Main

In making their claim, Strukov et al. therefore overlook the magneto-electric literature. In magneto-electric systems, the link arises explicitly and through a simple geometry, whereas Strukov et al. consider a system in which magnetic signals are neither applied nor measured. Moreover, some magneto-electric systems display nonlinear coupling^6,7, which is necessary but not sufficient for memristance^1,2.