Order-disorder Transition Of Vortex Matter In α-mo_xge_(1-x) Films Probed By Noise

摘要

We measure voltage noise spectra S_V(f) generated by current-driven vortices at various fields B including the peak-effect regime for amorphous Mo_xGe_(1-x) films with Corbino-disk and striplike contact geometries. Field dependences of the critical current I_c and S_V(f) are nearly independent of contact geometries, indicating that edge effects are not important on static or dynamic vortex properties. This is in contrast to the result reported for NbSe_2 crystals with much larger thickness. S_V(f) at low frequency f exhibits a sharp peak just below the peak field B_p of I_c, where the characteristic time of vortex motion increases significantly. The results suggest the existence of the order-disorder transition and vortex instabilities due to coexisting vortex phases at around B_p.