Effect of electron doping the metamagnet Sr_3-yLa_yRu₂O₇

We study the effects of adding electrons to the conduction bands of the itinerant metamagnet Sr(3)Ru(2)O(7) using substitution of La(3+) onto the Sr(2+) site. Small changes to the chemical potential have a large effect: adding only 0.03 electrons per Ru reduces the electronic specific-heat coefficient by 30%, but makes no corresponding change to the temperature (similar to 8 K) at which the electronic specific-heat coefficient shows its maximum. The observations are incompatible with a simple rigid-band shift, raising the possibility that a many-body resonance plays a key role in the physics of Sr(3)Ru(2)O(7)