365 research outputs found
Tunable Rashba spin-orbit interaction at oxide interfaces
The quasi-two-dimensional electron gas found at the LaAlO3/SrTiO3 interface
offers exciting new functionalities, such as tunable superconductivity, and has
been proposed as a new nanoelectronics fabrication platform. Here we lay out a
new example of an electronic property arising from the interfacial breaking of
inversion symmetry, namely a large Rashba spin-orbit interaction, whose
magnitude can be modulated by the application of an external electric field. By
means of magnetotransport experiments we explore the evolution of the
spin-orbit coupling across the phase diagram of the system. We uncover a steep
rise in Rashba interaction occurring around the doping level where a quantum
critical point separates the insulating and superconducting ground states of
the system
Seebeck effect in the conducting LaAlO_{3}/SrTiO_{3} interface
The observation of metallic behavior at the interface between insulating
oxides has triggered worldwide efforts to shed light on the physics of these
systems and clarify some still open issues, among which the dimensional
character of the conducting system. In order to address this issue, we measure
electrical transport (Seebeck effect, Hall effect and conductivity) in
LaAlO_{3}/SrTiO_{3} interfaces and, for comparison, in a doped SrTiO_{3} bulk
single crystal. In these experiments, the carrier concentration is tuned, using
the field effect in a back gate geometry. The combined analysis of all
experimental data at 77 K indicates that the thickness of the conducting layer
is ~7 nm and that the Seebeck effect data are well described by a
two-dimensional (2D) density of states. We find that the back gate voltage is
effective in varying not only the charge density, but also the thickness of the
conducting layer, which is found to change by a factor of ~2, using an electric
field between -4 and +4MV/m at 77K. No enhancement of the Seebeck effect due to
the electronic confinement and no evidence for two-dimensional quantization
steps are observed at the interfaces.Comment: 15 pages, 5 figure
Measurement Of The Nonlinear Ultrasonic Parameter In Aqueous Solutions
This paper deals with the measurement of the nonlinear ultrasound coefficient in aqueous solutions. Our aim is to show the possibility of using this parameter in ultrasound characterization of these solutions with the possibility of extending this technique to other complex media. The experimental determination of nonlinearity parameter is based on the quasi-linear approximation that allows us to derive an analytical expression of the second harmonic amplitude that takes into account the diffraction and the absorption effects. The experimental set up is composed of a piezoelectric disc transmitting at the fundamental frequency 2.2 MHz. The second harmonic is detected using a ring surrounding the disc and functioning at 4.4 MHz. The disc and the ring are both mounted on the same composed device and are both located in the same transversal plan to the propagation axis. The transmitted wave propagates through the sample and is detected by the receiver An appropriate signal processing permits the determination of the nonlinear parameter. The experimental results are promising and show a close correlation between the nonlinearity parameter, and the nature and the concentration of the compounds in the aqueous solutions studied.This paper deals with the measurement of the nonlinear ultrasound coefficient in aqueous solutions. Our aim is to show the possibility of using this parameter in ultrasound characterization of these solutions with the possibility of extending this technique to other complex media. The experimental determination of nonlinearity parameter is based on the quasi-linear approximation that allows us to derive an analytical expression of the second harmonic amplitude that takes into account the diffraction and the absorption effects. The experimental set up is composed of a piezoelectric disc transmitting at the fundamental frequency 2.2 MHz. The second harmonic is detected using a ring surrounding the disc and functioning at 4.4 MHz. The disc and the ring are both mounted on the same composed device and are both located in the same transversal plan to the propagation axis. The transmitted wave propagates through the sample and is detected by the receiver An appropriate signal processing permits the determination of the nonlinear parameter. The experimental results are promising and show a close correlation between the nonlinearity parameter, and the nature and the concentration of the compounds in the aqueous solutions studied
Epitaxial growth and thermodynamic stability of SrIrO3/SrTiO3 heterostructures
Obtaining high-quality thin films of 5d transition metal oxides is essential
to explore the exotic semimetallic and topological phases predicted to arise
from the combination of strong electron correlations and spin-orbit coupling.
Here, we show that the transport properties of SrIrO3 thin films, grown by
pulsed laser deposition, can be optimized by considering the effect of
laser-induced modification of the SrIrO3 target surface. We further demonstrate
that bare SrIrO3 thin films are subject to degradation in air and are highly
sensitive to lithographic processing. A crystalline SrTiO3 cap layer deposited
in-situ is effective in preserving the film quality, allowing us to measure
metallic transport behavior in films with thicknesses down to 4 unit cells. In
addition, the SrTiO3 encapsulation enables the fabrication of devices such as
Hall bars without altering the film properties, allowing precise
(magneto)transport measurements on micro- and nanoscale devices.Comment: 5 pages, 3 figure
Two-dimensional quantum oscillations of the conductance at LaAlO3/SrTiO3 interfaces
We report on a study of magnetotransport in LaAlO3/SrTiO3 interfaces
characterized by mobilities of the order of several thousands cm/Vs. We
observe Shubnikov-de Haas oscillations that indicate a two-dimensional
character of the Fermi surface. The frequency of the oscillations signals a
multiple sub-bands occupation in the quantum well or a multiple valley
configuration. From the temperature dependence of the oscillation amplitude we
extract an effective carrier mass \,. An electric field
applied in the back-gate geometry increases the mobility, the carrier density
and the oscillation frequency.Comment: 4 pages, 4 figure
Superconductivity at the LaAlO3/SrTiO3interface
We report on the structural characterization of LaAlO3/SrTiO3 interfaces and
on their transport properties. LaAlO3 films were prepared using pulsed laser deposition
onto TiO2 terminated (001) SrTiO3 substrates inducing a metallic conduction at the
interface. Resistance and Hall effect measurements reveal a sheet carrier density between
0.4 and 1.2·10 14 electrons/cm 2 at room temperature and mobility of ∼ 300 cm 2 V −1 s −1 at low temperatures. A transition to a superconducting state is observed at a temperature of ∼ 200 mK. The superconducting characteristics display signatures of 2D superconductivity
Diodes with Breakdown Voltages Enhanced by the Metal-Insulator Transition of LaAlO-SrTiO Interfaces
Using the metal-insulator transition that takes place as a function of
carrier density at the LaAlO-SrTiO interface, oxide diodes have been
fabricated with room-temperature breakdown voltages of up to 200 V. With
applied voltage, the capacitance of the diodes changes by a factor of 150. The
diodes are robust and operate at temperatures up to 270 C
Electrostatically tuned quantum superconductor-metal-insulator transition at the LaAlO3/SrTiO3 interface
Recently superconductivity at the interface between the insulators LaAlO3 and
SrTiO3 has been tuned with the electric field effect to an unprecedented range
of transition temperatures. Here we perform a detailed finite size scaling
analysis to explore the compatibility of the phase transition line with
Berezinskii-Kosterlitz-Thouless (BKT) behavior and a 2D-quantum
phase(QP)-transition. In an intermediate regime, limited by a gate voltage
dependent limiting length, we uncover remarkable consistency with a
BKT-critical line ending at a metallic quantum critical point, separating a
weakly localized insulator from the superconducting phase. Our estimates for
the critical exponents of the 2D-QP-transition, z=1 and nu=0.66, suggest that
it belongs to the 3D-xy universality class.Comment: 10 pages, 10 figure
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