Using time- and spatially-resolved hard X-ray diffraction microscopy, the striking structural and electrical dynamics upon optical excitation of a single crystal of BaTiO3 are simultaneously captured on sub-nanoseconds and nanoscale within individual ferroelectric domains and across walls. A large emergent photo-induced electric field of up to 20 million volts per meter is discovered in a surface layer of the crystal, which then drives polarization and lattice dynamics that are dramatically dis- tinct in a surface layer versus bulk regions. A dynamical phase-field modeling (DPFM) method is developed that reveals the microscopic origin of these dynamics, leading to GHz polarization and elastic waves travelling in the crystal with sonic speeds and spatially varying frequencies. The ad- vance of spatiotemporal imaging and dynamical modeling tools open opportunities of disentangling ultrafast processes in complex mesoscale structures such as ferroelectric domains
Complex oxides and strongly correlated electron systems are at the forefront of science due to their exquisite potential for optical, spintronic, transducing/actuating, multiferroic, electrochemical, and superconducting property enhancements. Accordingly, at the nanoscale, engineering of complex oxide compounds is a promising route for discovery of novel quantum functionalities in a vast space of synthesis technique, calling for high-resolution control and visualization of physical properties and their structural basis. The advent of optical pulse techniques and related instrumentation advances is used to access dynamical separation of correlated orders that hide at equilibrium and also to create novel phases, not available via mainstream synthesis techniques. In this this talk, I will discuss resonant and non-resonant spectroscopic manipulation of phase transitions in nanoferroic oxides, focusing on ultrafast optical creation of artificial supercrystals in epitaxial superlattices. While table top nonlinear optical techniques are used to access the ferroic properties, synchrotron based time-resolved structural techniques, including diffraction and spectroscopy are decisive tools for revealing the nature of orderings in superstructures, their symmetries, phase quantification and spatial distribution with sub-micron resolution.
Cross-sectional scanning tunneling microscopy (XSTM) is developed for studying the interfaces of the complex
oxide heterostructures. Since most of the complex oxide materials have a perovskite structure, which does not have
cleavage plane, it posed an experimental challenge for utilizing STM on the fractured surfaces. A well-controlled method
for fracturing non-cleavable materials was developed by using the common subtrate: Nb-doped SrTiO3 (Nb:STO).
Through systematically studies on the control of the fracturing conditions, on the tip-sample interactions and on the
resulting fractured surfaces of Nb:STO, atomic flat terraces are routinely created and stable measurements are achieved.
By harnessing the well-controlled fracturing method and the well-controlled tip conditions to a thin film system,
La2/3Ca1/3MnO3/Nb:STO (LCMO/Nb:STO), XSTM as well as the ability of cross-sectional scanning tunneling
spectroscopy (XSTS) directly revealed the band diagram mapping across the interface. The novel developed, well-controlled
XSTM/S for the interfaces of complex oxide heterostructures opened a door for accurate determination of
local electronic properties across and at the interface.
By using X-ray resonant magnetic scattering, the correlation of magnetic domains taken vertically in a Co/Cr/Co magnetic trilayer can be statistically quantified as a function of applied magnetic field. From these scans and from element specific magnetic hysteresis loops, we can identify the presence of both interlayer anti-ferromagnetic exchange coupling and ferromagnetic dipolar coupling within the trilayer.