Imaging competing electronic phases during metal insulator transitions in transition metal oxides using microwave impedance microscopy




Gangshettiwar, Ashish

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Metal-Insulator transitions are accompanied by huge resistivity changes, sometimes over ten orders of magnitude, and are widely observed in condensed-matter systems. Particularly important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is known as the Mott Insulator. Despite a long history of investigations, the driving force of the MIT and the exact nature of the ground state are still controversial. Using microwave impedance microscopy, we will study the coexisting metallic and insulating phases in different strongly correlated compounds which might carry important information on the transition in these materials. In this dissertation, I will begin by discussing Microwave Impedance Microscopy which will be the prime research tool used in the study of these materials. I will present the technical specifications of this tool and how it can be modified to be used on cryogenic setups, mainly, using tuning fork microscopy for topography feedback. The application of MIM to study Metal-Insulator Phase transitions in strongly correlated systems is demonstrated by studying doped Ruthenate oxides. Chapter 4 describes the insights gathered on Ti doped Bilayer Calcium Ruthenates which includes the discovery of a new stripe-phase at the MIT phase boundary. Followed by a chapter discussing the comparison with the MIT in Mn-doped bilayer Calcium ruthenate. I will conclude the dissertation with a short summary of our contribution to the field and an outlook where I would highlight the directions needed to pursue further research and come up with an overall picture of the phase transition in this class of material.



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