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

在强关联电子系统中，特别是巡游铁磁系统中，非常规超导电性(SC)经常出现在磁序的边缘。然而，据我们所知，基于调频基态的Molt跃迁体系的SC的报道很少。Ca2RuO4是一种具有反铁磁(AF)基态的Molt绝缘体，其U/W比Sr2RuO4大。在本项目中，我们发现Ca2RuO4在P~0.5 GPa时有金属-绝缘体转变：300K时从顺磁绝缘体转变为顺磁准2D金属，T[大于或等于]12K时从AF绝缘体转变为FM各向异性金属。当P[大于或等于]1 GPa时，a、b、c轴上的剩余磁化强度分别为~0.4、~0.3、~0.2μ_B。因此，a轴是易磁化方向，c轴是硬磁化方向。与定域Ru^&lt；4+&gt；离子的饱和磁矩2μ_B相比，较小的剩余磁化强度意味着-矩巡游Fm。T_c随P的增加而升高，在~5 GPa时达到25K，然后逐渐降低。T_c的外推，并提出在P&gt；10 Gpa处有一个调频量子临界点。因此，我们对P波Sc_2RuO_4与金属Ca_2RuO_4的FM之间的联系产生了浓厚的兴趣，并且与Q2D金属中巡回FM的性质进行了理论预测的比较也是有趣的。在加压Ca2RuO4中，P&lt；ab&gt；(T)表现为金属导电，而P_c(T)表现为非金属导电。这种Q2D性质被P增强了。与我们最近对SRO中Shubnikov-de Haas效应的P研究类似，表明在Ru214系统中，随着加压，费米表面片变得更加2D。也就是说，P使α和γ薄膜中的双费米面翘曲减小。我们推断，c轴电导与HTC一样，主要是由隧道机制描述的。

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.