Critical dynamic vortex fluctuations amidst a nascent peak effect in granular CeRu2 films

A peak effect has been investigated in granular CeRu2 films, grown via the method of pulsed laser deposition. The films exhibit residual resistivities and low field pinning force densities comparable to those for single crystals, yet the peak effect is not readily observable in electrical resistivity, ρ(H,T), or magnetization, M(H), measurements. The emergence of an increase in pinning force density corresponding to the known region of the peak effect is observed in films with larger grain size (d∼10 μm). Furthermore, in the large grain size films, within the region of enhanced pinning, scaling properties of voltage-current, V-I, data indicate a suppression of the superfluid density with a maximum corresponding to the pinning force peak. This phenomenon is seen to correspond to an anomalous feature found by Yoshizawa et al (1997 J. Phys. Soc. Japan 66 2355) in the transverse elastic moduli (c11-c12)/2 of single crystals, and to anomalous magnetostriction effects observed by Tachiki et al (1996 Z. Phys. B 100 369), and is consistent with an anomalous enhancement of the magnetic penetration depth observed by Yamashita et al (1997 Phys. Rev. Lett. 79 3771). A conventional explanation of the peak effect in CeRu2 based upon structural/electronic fluctuations is proposed. Additional evidence indicates that the enhanced ability of the vortices to couple to the atomic lattice, made possible by the softness of the transverse atomic moduli, and the collective critical behavior of the vortices, may also play an important role in the peak effect mechanism