Critical dynamic vortex fluctuations amidst a nascent peak effect in granularCeRu2 films

Abstract

A peak effect has been investigated in granularCeRu2 films, grown via the method of pulsed laser deposition. The films exhibit residualresistivities and low field pinning force densities comparable to those for singlecrystals, yet the peak effect is not readily observable in electrical resistivity,ρ(H,T), ormagnetization, M(H), measurements. The emergence of an increase in pinning force density corresponding tothe 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 regionof enhanced pinning, scaling properties of voltage–current,V–I, data indicate a suppression of the superfluid density with a maximum corresponding tothe pinning force peak. This phenomenon is seen to correspond to an anomalous featurefound 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 byTachiki et al (1996 Z. Phys. B 100 369), and is consistent with an anomalousenhancement of the magnetic penetration depth observed by Yamashita et al (1997 Phys. Rev. Lett. 79 3771). A conventional explanation of the peak effect inCeRu2 based upon structural/electronic fluctuations is proposed. Additional evidence indicatesthat the enhanced ability of the vortices to couple to the atomic lattice, made possible bythe softness of the transverse atomic moduli, and the collective critical behaviorof the vortices, may also play an important role in the peak effect mechanism.