Effects of gradient disorder on persistent currents in two-dimensional mesoscopic rings

Taking into account the gradient decay of the real disorder, we explore the effects of the disorder gradient and the structure sizes on persistent currents in the disorderorder twodimensional mesoscopic ring system, within the tightbinding model. In the absence of disorder gradient, the persistent current firstly decreases and then increases with disorder strength, indicating a localizedballisticlike transition existing there. In the presence of disorder gradient, the persistent current is decreased, due to the stronger disorder scattering in the surface disorder region of lower disorder strength. In the case of exponentially decaying disorder, especially, the localizedballisticlike transition disappeared, meaning that its observability depends on the distribution of the gradient disorder. In addition, the effects of both the ring width and the penetration depth of the disorder on persistent currents are explored, showing a strange quantum sizeeffect, which is different from previous results.