26,406 research outputs found
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
Form Factors Calculated on the Light-Front
A consistent treatment of decay is given on the
light-front. The to transition form factors are calculated in the
entire physical range of momentum transfer for the first time. The
valence-quark contribution is obtained using relativistic light-front wave
functions. Higher quark-antiquark Fock-state of the -meson bound state is
represented effectively by the configuration, and its effect
is calculated in the chiral perturbation theory. Wave function renormalization
is taken into account consistently. The contribution dominates
near the zero-recoil point ( GeV), and decreases rapidly as
the recoil momentum increases. We find that the calculated form factor
follows approximately a dipole -dependence in the entire range
of momentum transfer.Comment: Revtex, 19 pages, 9 figure
Temperature Dependent Polarity Reversal in Au/Nb:SrTiO3 Schottky Junctions
We have observed temperature-dependent reversal of the rectifying polarity in
Au/Nb:SrTiO3 Schottky junctions. By simulating current-voltage characteristics
we have found that the permittivity of SrTiO3 near the interface exhibits
temperature dependence opposite to that observed in the bulk, significantly
reducing the barrier width. At low temperature, tunneling current dominates the
junction transport due both to such barrier narrowing and to suppressed thermal
excitations. The present results demonstrate that novel junction properties can
be induced by the interface permittivity
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
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
The radiation from slots in truncated dielectric-covered surfaces
A theoretical approach based on the geometrical theory of diffraction is used to study the electromagnetic radiation from a narrow slot in a dielectric-covered perfectly-conducting surface terminated at an edge. The total far-zone field is composed of a geometrical optics field and a diffracted field. The geometrical optics field is the direct radiation from the slot to the field point. The slot also generates surface waves which are incident at the termination of the dielectric cover, where singly-diffracted rays and reflected surface waves are excited. The diffraction and reflection coefficients are obtained from the canonical problem of the diffraction of a surface wave by a right-angle wedge where the dielectric-covered surface is approximated by an impedance surface. This approximation is satisfactory for a very thin cover; however, the radiation from its vertical and faces cannot be neglected in treating the thicker dielectric cover. This is taken into account by using a Kirchhoff-type approximation, which contributes a second term to the diffraction coefficient previously obtained. The contributions from the geometrical optics field, the singly-diffracted rays and all significant multiply-diffracted rays are summed to give the total radiation. Calculated and measured patterns are found to be in good agreement
Electronic charges and electric potential at LaAlO3/SrTiO3 interfaces studied by core-level photoemission spectroscopy
We studied LaAlO3/SrTiO3 interfaces for varying LaAlO3 thickness by
core-level photoemission spectroscopy. In Ti 2p spectra for conducting "n-type"
interfaces, Ti3+ signals appeared, which were absent for insulating "p-type"
interfaces. The Ti3+ signals increased with LaAlO3 thickness, but started well
below the critical thickness of 4 unit cells for metallic transport. Core-level
shifts with LaAlO3 thickness were much smaller than predicted by the polar
catastrophe model. We attribute these observations to surface
defects/adsorbates providing charges to the interface even below the critical
thickness
- …