Pressure induced transition from Mott insulator to Q2D metal with ferromagnetic ground states

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Unconventional superconductivity (SC) has been frequently found on the border of magnetic order in strongly correlated electron systems, especially itinerant ferromagnetism (FM). However, there is few report on SC based on a Molt transition system with a FM ground state to our knowledge. Ca_2RuO_4, which has a larger U/W than Sr_2RuO_4, is a Molt insulator with an antiferromagnetic (AF) ground state. In this project, we found Ca_2RuO_4 features a metal-insulator transition at P〜0.5 GPa : at 300 K from paramagnetic insulator to paramagnetic quasi-2D metal ; at T【greater than or equal】12K from AF insulator to FM anisotropic metal. We obtain the remnant magnetisations along the a, b, and c axis are〜0.4,〜0.3,〜0.2μ_B at P【greater than or equal】1GPa, respectively. Thus, the a axis is easy direction of magnetisation and the c axis is hard direction. The small remnant magnetisation compared with the saturated moment 2μ_B of localized Ru^<4+> ion implies -moment itinerant FM. The T_c rises with increasing P reaching 25K at〜5GPa, then it decreases gradually. Extrapolation of Tc and suggests the induction of a FM quantum critical point at P>10GPa. We thus have strong interest in the connection between the p-wave SC Sr_2RuO_4, and the FM of metallic Ca_2RuO_4.Moreover, it is also interesting to compare to the properties of the itinerant FM in Q2D metal with theoretical predictions. In pressurised Ca_2RuO_4, P_<ab>(T) shows metallic conduction whereas P_c(T) exhibits a nonmetallic one. This Q2D nature is enhanced by P. Analogy with our recent P study of Shubnikov-de Haas effect in SRO suggests that the Fermi surface sheet becomes more 2D in Ru214 system with pressurising. Namely, P induces a reduction of a double Fermi-surface-warping in both the α and γ sheets. We infer that the c-axis conduction is mainly described by a tunnelling mechanism as in HTC.