Band-selective modification of the magnetic fluctuations in Sr₂RuO₄: A study of substitution effects

We report a study of magnetic, thermal, and transport properties of La3+ substituted Sr2RuO4, performed in order to investigate the effects of additional electron doping in this correlated metal. A gradual enhancement of the electronic part of specific heat and a more drastic increase of the static magnetic susceptibility were observed in Sr2-yLayRuO4 with increasing y. Furthermore, the quasi-two-dimensional Fermi-liquid behavior seen in pure Sr2RuO4 breaks down near the critical concentration y(c)similar to0.20. Combined with a realistic tight-binding model with rigid-band shift of Fermi level, the enhancement of the density of states can be ascribed to the elevation of the Fermi energy toward a van Hove singularity of the thermodynamically dominant gamma Fermi-surface sheet. On approaching the van Hove singularity, the effective nesting vector of the gamma band shrinks and further enhances the susceptibility near the wave vector qsimilar to0. We attribute the non-Fermi-liquid behavior to two-dimensional ferromagnetic fluctuations with short range correlations at the van Hove singularity. The observed behavior is in sharp contrast to that of Ti4+ substitution in Sr2RuO4 which enhances antiferromagnetic fluctuations and subsequently induces incommensurate magnetic ordering associated with the nesting between the other Fermi-surface sheets (alpha and beta). We thus establish that substitution of appropriate chemical dopants can band selectively modify the spin-fluctuation spectrum in the spin-triplet superconductor Sr2RuO4