493 research outputs found
Dramatic Mobility Enhancements in Doped SrTiO3 Thin Films by Defect Management
We report bulk-quality n-type SrTiO3 (n-SrTiO3) thin films fabricated by
pulsed laser deposition, with electron mobility as high as 6600 cm2 V-1 s-1 at
2 K and carrier density as low as 2.0 x 10^18cm-3 (~ 0.02 at. %), far exceeding
previous pulsed laser deposition films. This result stems from precise
strontium and oxygen vacancy defect chemistry management, providing a general
approach for defect control in complex oxide heteroepitaxy.Comment: 13 pages, 4 figure
Stoichiometry control of the electronic properties of the LaAlO_3/SrTiO_3 heterointerface
We investigate the effect of the laser parameters of pulsed laser deposition
on the film stoichiometry and electronic properties of LaAlO_3/SrTiO_3 (001)
heterostructures. The La/Al ratio in the LaAlO_3 films was varied over a wide
range from 0.88 to 1.15, and was found to have a strong effect on the interface
conductivity. In particular, the carrier density is modulated over more than
two orders of magnitude. The film lattice expansion, caused by cation
vacancies, is found to be the important functional parameter. These results can
be understood to arise from the variations in the electrostatic boundary
conditions, and their resolution, with stoichiometry.Comment: 4 pages, 3 figures, submitted for publicatio
Fermi surface and superconductivity in low-density high-mobility {\delta}-doped SrTiO3
The electronic structure of low-density n-type SrTiO3 delta-doped
heterostructures is investigated by angular dependent Shubnikov-de Haas
oscillations. In addition to a controllable crossover from a three- to
two-dimensional Fermi surface, clear beating patterns for decreasing dopant
layer thicknesses are found. These indicate the lifting of the degeneracy of
the conduction band due to subband quantization in the two-dimensional limit.
Analysis of the temperature-dependent oscillations shows that similar effective
masses are found for all components, associated with the splitting of the light
electron pocket. The dimensionality crossover in the superconducting state is
found to be distinct from the normal state, resulting in a rich phase diagram
as a function of dopant layer thickness.Comment: 4 pages, 5 figures, submitted for publicatio
Negative Differential Resistance Induced by Mn Substitution at SrRuO3/Nb:SrTiO3 Schottky Interfaces
We observed a strong modulation in the current-voltage characteristics of
SrRuO/Nb:SrTiO Schottky junctions by Mn substitution in SrRuO,
which induces a metal-insulator transition in bulk. The temperature dependence
of the junction ideality factor indicates an increased spatial inhomogeneity of
the interface potential with substitution. Furthermore, negative differential
resistance was observed at low temperatures, indicating the formation of a
resonant state by Mn substitution. By spatially varying the position of the Mn
dopants across the interface with single unit cell control, we can isolate the
origin of this resonant state to the interface SrRuO layer. These results
demonstrate a conceptually different approach to controlling interface states
by utilizing the highly sensitive response of conducting perovskites to
impurities
Dominant mobility modulation by the electric field effect at the LaAlO_3 / SrTiO_3 interface
Caviglia et al. [Nature (London) 456, 624 (2008)] have found that the
superconducting LaAlO_3 / SrTiO_3 interface can be gate modulated. A central
issue is to determine the principal effect of the applied electric field. Using
magnetotransport studies of a gated structure, we find that the mobility
variation is almost five times as large as the sheet carrier density.
Furthermore, superconductivity can be suppressed at both positive and negative
gate bias. These results indicate that the relative disorder strength strongly
increases across the superconductor-insulator transition.Comment: 4 pages, 4 figure
Coexistence of two- and three-dimensional Shubnikov-de Haas oscillations in Ar^+ -irradiated KTaO_3
We report the electron doping in the surface vicinity of KTaO_3 by inducing
oxygen-vacancies via Ar^+ -irradiation. The doped electrons have high mobility
(> 10^4 cm^2/Vs) at low temperatures, and exhibit Shubnikov-de Haas
oscillations with both two- and three-dimensional components. A disparity of
the extracted in-plane effective mass, compared to the bulk values, suggests
mixing of the orbital characters. Our observations demonstrate that Ar^+
-irradiation serves as a flexible tool to study low dimensional quantum
transport in 5d semiconducting oxides
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
Metal-to-insulator transition in anatase TiO2 thin films induced by growth rate modulation
We demonstrate control of the carrier density of single phase anatase TiO2
thin films by nearly two orders of magnitude by modulating the growth kinetics
during pulsed laser deposition, under fixed thermodynamic conditions. The
resistivity and the intensity of the photoluminescence spectra of these TiO2
samples, both of which correlate with the number of oxygen vacancies, are shown
to depend strongly on the growth rate. A quantitative model is used to explain
the carrier density changes.Comment: 13 pages 3 figure
Thickness dependence of the mobility at the LaAlO_3 / SrTiO_3 interface
The electronic transport properties of a series of LaAlO_3 / SrTiO_3
interfaces were investigated, and a systematic thickness dependence of the
sheet resistance and magnetoresistance was found for constant growth
conditions. This trend occurs above the critical thickness of four unit cells,
below which the LaAlO_3 / SrTiO_3 interface is not conducting. A dramatic
decrease in mobility of the electron gas of nearly two orders of magnitude was
observed with increasing LaAlO_3 thickness from five to 25 unit cells.Comment: 3 pages, 4 figures, submitted for publicatio
- …