Unveiling the physical origin of the electro-plasticity of metals

It has been widely known that the plasticity of metals enhances under electric current. Such electro-plasticity has been utilized for various industrial purposes. Even until recently, Joule heating was mostly regarded as the origin of this phenomenon, but it turned out that the temperature raised in this phenomenon may not be high enough to explain the enhanced plasticity. In this work, we unveil the physical origin of such electro-plasticity using first-principle calculation. We investigate the effects of extra charges supplied by the current on phonon properties and shear deformation. We reveal that bulk phonon properties change little with a small amount of supplied charges. On the other hand, extra charges affect quite considerably the phonon properties of imperfect structures like a slab system or a system with grain boundaries resulting in significant phonon softening. Additionally, we discover that extra charges can reduce the energy barrier of shear motions in various metal slabs. Eventually, we suggest that electro-plasticity originates from local charge accumulation or deficiency occurring in imperfect regions.