In single crystals of $2\mathrm{H}\mathrm{\text{−}}{\mathrm{NbSe}}_2$, we identify for the first time a crossover from a weak collective to a strong pinning regime in the vortex state which is not associated with the peak effect phenomenon. Instead, we find the crossover is associated with an anomalous history dependent magnetization response. In the dc magnetic field ($B_{\mathrm{dc}}$)-temperature ($T$) vortex matter phase diagram we demarcate this pinning crossover boundary. We also delineate another boundary which separates the strong pinning region from a thermal fluctuation dominated regime, and find that a peak effect appears on this boundary.

• Received 28 June 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.027003