310 research outputs found
Charge writing at the LaAlO3/SrTiO3 surface
Biased conducting-tip atomic force microscopy (AFM) has been shown to write
and erase nanoscale metallic lines at the LaAlO3/SrTiO3 interface. Using
various AFM modes, we show the mechanism of conductivity switching is the
writing of surface charge. These charges are stably deposited on a wide range
of LaAlO3 thicknesses, including bulk crystals. A strong asymmetry with writing
polarity was found for 1 and 2 unit cells of LaAlO3, providing experimental
evidence for a theoretically predicted built-in potential.Comment: 12 pages, 4 figures, plus supplementary information, submitted to
Nano Letter
Nonlinear two-dimensional terahertz photon echo and rotational spectroscopy in the gas phase
Ultrafast two-dimensional spectroscopy utilizes correlated multiple
light-matter interactions for retrieving dynamic features that may otherwise be
hidden under the linear spectrum. Its extension to the terahertz regime of the
electromagnetic spectrum, where a rich variety of material degrees of freedom
reside, remains an experimental challenge. Here we report ultrafast
two-dimensional terahertz spectroscopy of gas-phase molecular rotors at room
temperature. Using time-delayed terahertz pulse pairs, we observe photon echoes
and other nonlinear signals resulting from molecular dipole orientation induced
by three terahertz field-dipole interactions. The nonlinear time-domain
orientation signals are mapped into the frequency domain in two-dimensional
rotational spectra which reveal J-state-resolved nonlinear rotational dynamics.
The approach enables direct observation of correlated rotational transitions
and may reveal rotational coupling and relaxation pathways in the ground
electronic and vibrational state.Comment: 31 pages, 14 figure
Termination Control of the Interface Dipole in LaSrMnO/Nb:SrTiO (001) Schottky Junctions
In order to investigate the interface termination dependence of perovskite
band alignments, we have studied the Schottky barrier height at
LaSrMnO/Nb:SrTiO (001) heterointerfaces. As the
Nb:SrTiO semiconductor was varied from TiO termination to SrO
termination by variable insertion of a SrMnO layer, a large systematic
increase in the Schottky barrier height was observed. This can be ascribed to
the evolution of the interface dipole induced to screen the polar discontinuity
at the interface, which gives a large internal degree of freedom for tuning
band diagrams in oxides.Comment: 10 pages, 5 figure
Nonlinear terahertz metamaterials via field-enhanced carrier dynamics in GaAs
We demonstrate nonlinear metamaterial split ring resonators (SRRs) on GaAs at
terahertz frequencies. For SRRs on doped GaAs films, incident terahertz
radiation with peak fields of ~20 - 160 kV/cm drives intervalley scattering.
This reduces the carrier mobility and enhances the SRR LC response due to a
conductivity decrease in the doped thin film. Above ~160 kV/cm, electric field
enhancement within the SRR gaps leads to efficient impact ionization,
increasing the carrier density and the conductivity which, in turn, suppresses
the SRR resonance. We demonstrate an increase of up to 10 orders of magnitude
in the carrier density in the SRR gaps on semi-insulating GaAs substrate.
Furthermore, we show that the effective permittivity can be swept from negative
to positive values with increasing terahertz field strength in the impact
ionization regime, enabling new possibilities for nonlinear metamaterials.Comment: 5 pages, 4 figure
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