35 research outputs found
On the persistence of polar domains in ultrathin ferroelectric capacitors
The instability of ferroelectric ordering in ultra-thin films is one of the
most important fundamental issues pertaining realization of a number of
electronic devices with enhanced functionality, such as ferroelectric and
multiferroic tunnel junctions or ferroelectric field effect transistors. In
this paper, we investigate the polarization state of archetypal ultrathin
(several nanometres) ferroelectric heterostructures: epitaxial
single-crystalline BaTiO films sandwiched between the most habitual
perovskite electrodes, SrRuO, on top of the most used perovskite substrate,
SrTiO. We use a combination of piezoresponse force microscopy, dielectric
measurements and structural characterization to provide conclusive evidence for
the ferroelectric nature of the relaxed polarization state in ultrathin
BaTiO capacitors. We show that even the high screening efficiency of
SrRuO electrodes is still insufficient to stabilize polarization in
SrRuO/BaTiO/SrRuO heterostructures at room temperature. We identify
the key role of domain wall motion in determining the macroscopic electrical
properties of ultrathin capacitors and discuss their dielectric response in the
light of the recent interest in negative capacitance behaviour.Comment: 13 pages, 4 figure
"Water-cycle" mechanism for writing and erasing nanostructures at the LaAlO3/SrTiO3 interface
Nanoscale control of the metal-insulator transition in LaAlO3/ SrTiO3
heterostructures can be achieved using local voltages applied by a conductive
atomic-force microscope probe. One proposed mechanism for the writing and
erasing process involves an adsorbed H2O layer at the top LaAlO3 surface. In
this picture, water molecules dissociates into OH- and H+ which are then
selectively removed by a biased AFM probe. To test this mechanism, writing and
erasing experiments are performed in a vacuum AFM using various gas mixtures.
Writing ability is suppressed in those environments where H2O is not present.
The stability of written nanostructures is found to be strongly associated with
the ambient environment. The self-erasure process in air can be strongly
suppressed by creating a modest vacuum or replacing the humid air with dry
inert gas. These experiments provide strong constraints for theories of both
the writing process as well as the origin of interfacial conductance.Comment: 11 pages, 3 figure
Anomalous Transport in Sketched Nanostructures at the LaAlO3/SrTiO3 Interface
The oxide heterostructure LaAlO3/SrTiO3 supports a two-dimensional electron
liquid with a variety of competing phases including magnetism,
superconductivity and weak antilocalization due to Rashba spin-orbit coupling.
Further confinement of this 2D electron liquid to the quasi-one-dimensional
regime can provide insight into the underlying physics of this system and
reveal new behavior. Here we describe magnetotransport experiments on narrow
LaAlO3/SrTiO3 structures created by a conductive atomic force microscope
lithography technique. Four-terminal local transport measurements on
~10-nm-wide Hall bar structures yield longitudinal resistances that are
comparable to the resistance quantum h/e2 and independent of the channel
length. Large nonlocal resistances (as large as 10^4 ohms) are observed in some
but not all structures with separations between current and voltage that are
large compared to the 2D mean-free path. The nonlocal transport is strongly
suppressed by the onset of superconductivity below ~200 mK. The origin of these
anomalous transport signatures is not understood, but may arise from coherent
transport defined by strong spin-orbit coupling and/or magnetic interactions