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Abstract:
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.
