31 research outputs found
Stripe charge ordering in SrO-terminated SrTiO3(001) surfaces
The local electronic structure of the SrO-terminated SrTiO3(001) surface was
explored using scanning tunneling microscopy. At low bias voltages in the empty
states, a unidirectional structure with a periodicity of 3 unit cells,
superimposed on a c(2 x 2) reconstructed structure, was found to develop along
the crystallographic a axis. This structure indicates a charge-ordered stripe
induced by carrier doping from oxygen vacancies in the SrO and the subsurface
TiO2 planes. In the filled states, localized deep in-gap states were observed
in addition to large energy gaps in the tunneling spectra. This result
represents inelastic tunneling due to significant electron-lattice interaction
associated with unidirectional lattice distortion in the SrO-terminated
surface.Comment: 6 pages, 5 figures, accepted for publication in PR
Atomically Resolved Surface Structure of SrTiO3(001) Thin Films Grown in Step-Flow Mode by Pulsed Laser Deposition
The surface structure of SrTiO3(001) thin films homoepitaxially grown by PLD
in step-flow mode was characterized using low temperature STM. It was found
that one-dimensional (1D) TiOx-based nanostructures were formed on the thin
film surface and their density increased with increasing thin film thickness.
Most of the 1D nanostructures disappeared after a post-deposition annealing,
indicating that this structure is metastable due to the nonequilibrium growth
mode. The resulting surface after annealing exhibited similar features to that
of a thinner film, having a domain structure with (2x1) and (1x2)
reconstructions, but with fewer oxygen-vacancy-type defects. These results
imply that the step-flow growth is likely to produce TiOx-rich surface and Ti
deficiencies in the film. By the post-deposition annealing, the rich TiOx would
diffuse from the surface into the film to compensate defects associated with Ti
vacancies and oxygen vacancies, resulting in the stable surface structure with
fewer oxygen vacancies. Thus, STM measurements can provide us with a
microscopic picture of surface stoichiometry of thin films originating in the
dynamics of the growth process, and can present a new approach for designing
functional oxide films.Comment: 12 pages, 4 figure
Time-resolved force microscopy using delay-time modulation method
We developed a time-resolved force microscopy technique by integrating atomic
force microscopy using a tuning-fork-type cantilever with the delay time
modulation method for optical pump-probe light. We successfully measured the
dynamics of surface recombination and diffusion of photoexcited carriers in
bulk WSe2, which is challenging owing to the effect of tunneling current in
time-resolved scanning tunneling microscopy. The obtained results were
comprehensively explained with the model based on the dipole-dipole interaction
induced by photo illumination.Comment: 13 pages, 4 figure
Atomic-scale visualization of initial growth of homoepitaxial SrTiO3 thin film on an atomically ordered substrate
The initial homoepitaxial growth of SrTiO3 on a (\surd13\times\surd13) -
R33.7{\deg}SrTiO3(001) substrate surface, which can be prepared under oxide
growth conditions, is atomically resolved by scanning tunneling microscopy. The
identical (\surd13\times\surd13) atomic structure is clearly visualized on the
deposited SrTiO3 film surface as well as on the substrate. This result
indicates the transfer of the topmost Ti-rich (\surd13\times\surd13) structure
to the film surface and atomic-scale coherent epitaxy at the film/substrate
interface. Such atomically ordered SrTiO3 substrates can be applied to the
fabrication of atom-by-atom controlled oxide epitaxial films and
heterostructures
Direct observation of the washboard noise of a driven vortex lattice in a high-temperature superconductor, Bi2Sr2CaCu2Oy
We studied the conduction noise spectrum in the vortex state of a
high-temperature superconductor, Bi2Sr2CaCu2Oy, subject to a uniform driving
force. Two characteristic features, a broadband noise (BBN) and a narrow-band
noise (NBN), were observed in the vortex-solid phase. The origin of the large
BBN was determined to be plastic motion of the vortices, whereas the NBN was
found to originate from the washboard modulation of the translational velocity
of the driven vortices. We believe this to be the first observation ofComment: 4 pages, 4 figures, to appear in Phys. Rev. Let
The electronic state of vortices in YBa2Cu3Oy investigated by complex surface impedance measurement
The electromagnetic response to microwaves in the mixed state of
YBa2Cu3Oy(YBCO) was measured in order to investigate the electronic state
inside and outside the vortex core. The magnetic-field dependence of the
complex surface impedance at low temperatures was in good agreement with a
general vortex dynamics description assuming that the field-independent viscous
damping force and the linear restoring force were acting on the vortices. In
other words, both real and imaginary parts of the complex resistivity, \rho_1,
and \rho_2, were linear in B. This is explained by theories for d-wave
superconductors. Using analysis based on the Coffey-Clem description of the
complex penetration depth, we estimated that the vortex viscosity \eta at 10 K
was (4 \sim 5) \times 10^{-7} Ns/m^2. This value corresponds to \omega_0 \tau
\sim 0.3 - 0.5, where \omega_0 and \tau are the minimal gap frequency and the
quasiparticle lifetime in the vortex core, respectively. These results suggest
that the vortex core in YBCO is in the moderately clean regime. Investigation
of the moderately clean vortex core in high-temperature superconductors is
significant because physically new effects may be expected due to d-wave
characteristics and to the quantum nature of cuprate superconductors. The
behavior of Z_s as a function of B across the first order transition (FOT) of
the vortex lattice was also investigated. Unlike Bi2Sr2CaCu2Oy (BSCCO), no
distinct anomaly was observed around the FOT in YBCO. Our results suggest that
the rapid increase of X_s due to the change of superfluid density at the FOT
would be observed only in highly anisotropic two-dimensional vortex systems
like BSCCO. We discuss these results in terms of the difference of the
interlayer coupling and the energy scale between the two materials.Comment: 10 pages, 6 figures, to be published in Phys. Rev. B, one reference
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