Emergence of Competing Stripe Phase near the Mott Transition in Ti-doped Bilayer Calcium Ruthenates*

The physics of nanoscale phase separation is at the heart of strongly correlated materials, where multiple degrees of freedom such as charge, spin, lattice, and orbital are simultaneously active. Using microwave impedance microscopy, we spatially resolved the coexisting phases on a Ca3(Ru0.9Ti0.1)2O7 bulk crystal during the metal-insulator transition. Different from a typical first- order phase transition where coexistence of the two terminal phases takes place, a new stripe phase oriented along the in-plane crystalline axes emerges inside both the G-type antiferromagnetic insulating state and paramagnetic metallic state. The effect of this electronic state can be observed in macroscopic measurements, allowing us to construct a phase diagram that takes into account the energetically competing phases. Our work provides a model approach to correlate macroscopic properties and mesoscopic phase separation in complex oxides.