Novel Angular Scaling of Vortex Phase Transitions inBi2Sr2CaCu2O8+y

Local magnetization measurements using micro-Hall probes in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+y}$ single crystals under various field angles $\theta$ from the $c$ axis reveal that the angular dependence of the first-order transition ( $H_{\mathrm{FOT}}$) and the second peak ( $H_p$) is clearly different from the conventional scaling law. Instead, we found a novel angular scaling, which is expressed as $H_{\mathrm{FOT}}{,H}_p\propto [\cos \theta +\alpha (T)\sin \theta {]}^{-1\mathrm{}}$ [ $\alpha \left(T\right)$: temperature dependent parameter] in a wide angle range. Two possible origins for this novel angular dependence are discussed: (1) The effect of the electromagnetic coupling between pancake vortices and (2) the suppression of the Josephson coupling by the in-plane field.