Multiple Metamagnetic Quantum Criticality in Sr3Ru2O7

Bilayer strontium ruthenate Sr3Ru2O7 displays pronounced non-Fermi liquid behavior at magnetic fields around 8 T, applied perpendicular to the ruthenate planes, which previously has been associated with an itinerant metamagnetic quantum critical end point (QCEP). We focus on the magnetic Gruneisen parameter Gamma(H), which is the most direct probe to characterize field-induced quantum criticality. We confirm quantum critical scaling due to a putative two-dimensional QCEP near 7.845(5) T, which is masked by two ordered phases A and B, identified previously by neutron scattering. In addition, we find evidence for a QCEP at 7.53 (2) T and determine the quantum critical regimes of both instabilities and the effect of their superposition.