Ashish Gangshettiwar, UT-Austin

"Imaging Metal-Insulator Phase Transition by Microwave Impedance Microscopy"

Abstract: 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. Rare-earth nickelate compounds (RNiO3, R = La … Lu) represent a textbook example in that the physical properties can be continuously tuned by structural properties. Sm0.5Nd0.5NiO3 (SNNO)is an interesting system in the RNiO3 family as it is close to the phase boundary of critical tolerance factor where TMI and TN become decoupled, in other words the system is highly susceptible to small external perturbations due to the competition among different energy scales to stabilize the electronic and magnetic ground states. 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 SNNO thin films which might carry important information on the transition in these materials. The devices are patterned by different techniques (overgrowth and etching). I will present the technical challenges to study these devices as well as the different MIT behavior observed in these samples. Furthermore, we plan to study thickness and strain dependence on the percolation observed around the transition point. Our future plans include investigating other materials (ruthenates and manganites) which show MIT under different stimuli (such as doping, temperature and magnetic field).