19 research outputs found
"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
Introduction to the absolute brightness and number statistics in spontaneous parametric down-conversion
As a tutorial, we examine the absolute brightness and number statistics of photon pairs generated in spontaneous parametric down-conversion (SPDC) from first principles. In doing so, we demonstrate how the diverse implementations of SPDC can be understood through a single common framework, and use this to derive straightforward formulas for the biphoton generation rate (pairs per second) in a variety of different circumstances. In particular, we consider the common cases of both collimated and focused Gaussian pump beams in a bulk nonlinear crystal, as well as in nonlinear waveguides and micro-ring resonators. Furthermore, we examine the number statistics of down-converted light using a non-perturbative approximation (the multi-mode squeezed vacuum), to provide quantitative formulas for the relative likelihood of multi-pair production events, and explore how the quantum state of the pump affects the subsequent statistics of the down-converted light. Following this, we consider the limits of the undepleted pump approximation, and conclude by performing experiments to test the effectiveness of our theoretical predictions for the biphoton generation rate in a variety of different sources
Rewritable nanoscale oxide photodetector
Nanophotonic devices seek to generate, guide, and/or detect light using
structures whose nanoscale dimensions are closely tied to their functionality.
Semiconducting nanowires, grown with tailored optoelectronic properties, have
been successfully placed into devices for a variety of applications. However,
the integration of photonic nanostructures with electronic circuitry has always
been one of the most challenging aspects of device development. Here we report
the development of rewritable nanoscale photodetectors created at the interface
between LaAlO3 and SrTiO3. Nanowire junctions with characteristic dimensions
2-3 nm are created using a reversible AFM writing technique. These nanoscale
devices exhibit a remarkably high gain for their size, in part because of the
large electric fields produced in the gap region. The photoconductive response
is gate-tunable and spans the visible-to-near-infrared regime. The ability to
integrate rewritable nanoscale photodetectors with nanowires and transistors in
a single materials platform foreshadows new families of integrated
optoelectronic devices and applications.Comment: 5 pages, 5 figures. Supplementary Information 7 pages, 9 figure