Quantum phase transitions in Ca3Ru2O7

The strongly correlated bilayer ruthenate Ca3Ru2O7 undergoes first a magnetic transition (TN=56 K, Q=(0,0,1/2)) and then a structural transition (TS=48 K) on cooling. At low temperature, this material exhibits very small Fermi surface pockets, consistent with its low carrier density. We follow the evolution of the low temperature state of Ca3Ru2O7 with pressure: The structural transition is rapidly suppressed, and TS extrapolates to zero at pc1≅35 kbar. The magnetic transition is also suppressed. TN extrapolates towards a critical pressure of pc2≅55 kbar, but above 40 kbar it is replaced by signatures of a new ordered phase with an onset temperature of about TX≅25 K. This new ordered phase, in turn, appears to be suppressed near pc3≅80 kbar. We explore the nature of the high pressure state of Ca3Ru2O7 in a series of high pressure measurements of the resistivity, magnetic susceptibility and magnetisation, and investigate, in particular, the vicinity of the quantum critical point, pc3.