Magnetic field-tuned quantum criticality in the metallic ruthenate Sr3Ru2O7

The concept of quantum criticality is proving to be central to attempts to understand the physics of strongly correlated electrons. Here, we argue tha t observations on the itinerant metamagnet Sr3Ru2O7 represent good evidence for a new class of quantum critical point, arising when the critical end p oint terminating a tine of first-order transitions is depressed toward zero temperature. This is of interest both in its own right and because of the convenience of having a quantum critical point for which the tuning paramet er is the magnetic field. The relationship between the resultant critical f luctuations and novel behavior very near the critical field is discussed.