CNMS RESEARCH

Imaging and manipulation of the competing electronic phases near the Mott metal-insulator transition

Tae-Hwan Kim1, M. Angst2, B. Hu3, R. Jin3, X. G. Zhang1,
J. F. Wendelken1, E. W. Plummer3, and An-Ping Li1

1Center for Nanophase Materials Sciences, Oak Ridge National Laboratory
2
Materials Science and Technology Division, Oak Ridge National Laboratory
3
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA

Strain-induced domain evolutions in the cleaved surface of a Sr3(Ru0.8Mn0.2)2O7. (A), Domain image before stress and (B),  after applying an uniaxial compressive stress in the ab plane. (C),  Domain evolution in time with nominal strain of 0.0022%. (D), Domain area change with time.

Achievement:

The complex interplay between electron and lattice degrees of freedom produces many nearly degenerate electronic states in correlated electron materials. These states determine the functionality of the system, but competition between these states produces highly variable properties whose mechanism remains in debate. By imaging phase domains with electron microscopy and interrogating individual domains in situ via point probe electron transport spectroscopy in double-layered Sr3(Ru1−xMnx )2O7 (x = 0 and 0.2), we show the first real-space evidence that the microscopic phase competition and the Mott-type metal-insulator transition can be tuned by applying a mechanical stress. Studies were enabled by novel application of a newly developed cryogenic four-probe scanning tunneling microscope system, which both images the microscopic phase domains using a scanning electron microscope and simultaneously interrogates the electronic properties of each domain using the scanning tunneling probes in either spectroscopic or transport modes. Dramatic changes were observed in the size and shape of phase domains in response to thermal cycling and mechanical stress.  A quantitative correlation between the macroscopic metal-insulator transition and the microscopic phase percolation has been revealed.

Significance:

This work presents the first direct, real-space, observation that a “gigantic” phase domain response to a minute amount of strain can occur in a Mott system. In contrast to the “conventional” way of tuning the Mott transition by chemical doping, we have now demonstrated tuning by strain, paving the way for new control of the electronic properties for electronics and sensing applications. The detailed images of the phase percolation and the dynamic phase competition enable further investigations on the strain control of emergent functionality in correlated electronic materials.

Credit:

This work was published in the Proceedings of the National Academy of Sciences.  This research at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. MA was supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. EWP was partially supported by DOE #DE-SC0002136.

Citation: “Imaging and manipulation of the competing electronic phases near the Mott metal-insulator transition”, Proceedings of the National Academy of Sciences 107, 5272. DOI: www.pnas.org/cgi/doi/10.1073/pnas.1000655107.