Local Density Fluctuations of Moving Vortices in the Solid and Liquid Phases inBi2Sr2CaCu2Oy

By a new method using a 2DEG micro-Hall probe, the local field noise generated by current-driven vortices was investigated around the vortex melting transition field $H_m$ in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_y$. A broad-band noise (BBN) was found to occur just when the pinned vortices start moving. When the vortex velocity increased, the BBN disappeared. In turn, a narrow-band noise appeared. These noises were observed in the liquid phase as well as in the solid phase. We conclude that in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_y$ the moving vortices in the solid and liquid phases fluctuate qualitatively in the same manner near $H_m$. This is a characteristic of the vortices in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_y$.