50 research outputs found
Extrinsic Spin Hall Effect Induced by Iridium Impurities in Copper
We study the extrinsic spin Hall effect induced by Ir impurities in Cu by
injecting a pure spin current into a CuIr wire from a lateral spin valve
structure. While no spin Hall effect is observed without Ir impurity, the spin
Hall resistivity of CuIr increases linearly with the impurity concentration.
The spin Hall angle of CuIr, % throughout the concentration
range between 1% and 12%, is practically independent of temperature. These
results represent a clear example of predominant skew scattering extrinsic
contribution to the spin Hall effect in a nonmagnetic alloy.Comment: 5 pages, 4 figure
Anisotropic charge dynamics in the quantum spin-liquid candidate -(BEDT-TTF)Cu(CN)
We have in detail characterized the anisotropic charge response of the dimer
Mott insulator -(BEDT-TTF)\-Cu(CN) by dc conductivity, Hall
effect and dielectric spectroscopy. At room temperature the Hall coefficient is
positive and close to the value expected from stoichiometry; the temperature
behavior follows the dc resistivity . Within the planes the dc
conductivity is well described by variable-range hopping in two dimensions;
this model, however, fails for the out-of-plane direction. An unusually broad
in-plane dielectric relaxation is detected below about 60 K; it slows down much
faster than the dc conductivity following an Arrhenius law. At around 17 K we
can identify a pronounced dielectric anomaly concomitantly with anomalous
features in the mean relaxation time and spectral broadening. The out-of-plane
relaxation, on the other hand, shows a much weaker dielectric anomaly; it
closely follows the temperature behavior of the respective dc resistivity. At
lower temperatures, the dielectric constant becomes smaller both within and
perpendicular to the planes; also the relaxation levels off. The observed
behavior bears features of relaxor-like ferroelectricity. Because
heterogeneities impede its long-range development, only a weak tunneling-like
dynamics persists at low temperatures. We suggest that the random potential and
domain structure gradually emerge due to the coupling to the anion network.Comment: 14 pages, 13 figure
Full oxide heterostructure combining a high-Tc diluted ferromagnet with a high-mobility conductor
We report on the growth of heterostructures composed of layers of the
high-Curie temperature ferromagnet Co-doped (La,Sr)TiO3 (Co-LSTO) with
high-mobility SrTiO3 (STO) substrates processed at low oxygen pressure. While
perpendicular spin-dependent transport measurements in STO//Co-LSTO/LAO/Co
tunnel junctions demonstrate the existence of a large spin polarization in
Co-LSTO, planar magnetotransport experiments on STO//Co-LSTO samples evidence
electronic mobilities as high as 10000 cm2/Vs at T = 10 K. At high enough
applied fields and low enough temperatures (H < 60 kOe, T < 4 K) Shubnikov-de
Haas oscillations are also observed. We present an extensive analysis of these
quantum oscillations and relate them with the electronic properties of STO, for
which we find large scattering rates up to ~ 10 ps. Thus, this work opens up
the possibility to inject a spin-polarized current from a high-Curie
temperature diluted oxide into an isostructural system with high-mobility and a
large spin diffusion length.Comment: to appear in Phys. Rev.
Co-doped (La,Sr)TiO3-d: a high-Curie temperature diluted magnetic system with large spin-polarization
We report on tunneling magnetoresistance (TMR) experiments that demonstrate
the existence of a significant spin polarization in Co-doped (La,Sr)TiO3-d
(Co-LSTO), a ferromagnetic diluted magnetic oxide system (DMOS) with high Curie
temperature. These TMR experiments have been performed on magnetic tunnel
junctions associating Co-LSTO and Co electrodes. Extensive structural analysis
of Co-LSTO combining high-resolution transmission electron microscopy and Auger
electron spectroscopy excluded the presence of Co clusters in the Co-LSTO layer
and thus, the measured ferromagnetism and high spin polarization are intrinsic
properties of this DMOS. Our results argue for the DMOS approach with complex
oxide materials in spintronics
Two-dimensional superconductivity at a Mott-Insulator/Band-Insulator interface: LaTiO3/SrTiO3
Transition metal oxides display a great variety of quantum electronic
behaviours where correlations often play an important role. The achievement of
high quality epitaxial interfaces involving such materials gives a unique
opportunity to engineer artificial structures where new electronic orders take
place. One of the most striking result in this area is the recent observation
of a two-dimensional electron gas at the interface between a strongly
correlated Mott insulator LaTiO3 and a band insulator SrTiO3. The mechanism
responsible for such a behaviour is still under debate. In particular, the
influence of the nature of the insulator has to be clarified. Here we show that
despite the expected electronic correlations, LaTiO3/SrTiO3 heterostructures
undergo a superconducting transition at a critical temperature Tc=300 mK. We
have found that the superconducting electron gas is confined over a typical
thickness of 12 nm. We discuss the electronic properties of this system and
review the possible scenarios
Rewritable nanoscale oxide photodetector
Nanophotonic devices seek to generate, guide, and/or detect light using
structures whose nanoscale dimensions are closely tied to their functionality.
Semiconducting nanowires, grown with tailored optoelectronic properties, have
been successfully placed into devices for a variety of applications. However,
the integration of photonic nanostructures with electronic circuitry has always
been one of the most challenging aspects of device development. Here we report
the development of rewritable nanoscale photodetectors created at the interface
between LaAlO3 and SrTiO3. Nanowire junctions with characteristic dimensions
2-3 nm are created using a reversible AFM writing technique. These nanoscale
devices exhibit a remarkably high gain for their size, in part because of the
large electric fields produced in the gap region. The photoconductive response
is gate-tunable and spans the visible-to-near-infrared regime. The ability to
integrate rewritable nanoscale photodetectors with nanowires and transistors in
a single materials platform foreshadows new families of integrated
optoelectronic devices and applications.Comment: 5 pages, 5 figures. Supplementary Information 7 pages, 9 figure
Mapping the Spatial Distribution of Charge Carriers in LaAlO3/SrTiO3 Heterostructures
At the interface between complex insulating oxides, novel phases with
interesting properties may occur, such as the metallic state reported in the
LaAlO3/SrTiO3 system. While this state has been predicted and reported to be
confined at the interface, some works indicate a much broader spatial
extension, thereby questioning its origin. Here we provide for the first time a
direct determination of the carrier density profile of this system through
resistance profile mappings collected in cross-section LaAlO3/SrTiO3 samples
with a conducting-tip atomic force microscope (CT-AFM). We find that, depending
upon specific growth protocols, the spatial extension of the high-mobility
electron gas can be varied from hundreds of microns into SrTiO3 to a few
nanometers next to the LaAlO3/SrTiO3 interface. Our results emphasize the
potential of CT-AFM as a novel tool to characterize complex oxide interfaces
and provide us with a definitive and conclusive way to reconcile the body of
experimental data in this system.Comment: This updated version contains new experimental dat
Gate-tunable giant nonreciprocal charge transport in noncentrosymmetric oxide interfaces
A polar conductor, where inversion symmetry is broken, may exhibit directional propagation of itinerant electrons, i.e., the rightward and leftward currents differ from each other, when time-reversal symmetry is also broken. This potential rectification effect was shown to be very weak due to the fact that the kinetic energy is much higher than the energies associated with symmetry breaking, producing weak perturbations. Here we demonstrate the appearance of giant nonreciprocal charge transport in the conductive oxide interface, LaAlO3/SrTiO3, where the electrons are confined to two-dimensions with low Fermi energy. In addition, the Rashba spin???orbit interaction correlated with the sub-band hierarchy of this system enables a strongly tunable nonreciprocal response by applying a gate voltage. The observed behavior of directional response in LaAlO3/SrTiO3 is associated with comparable energy scales among kinetic energy, spin???orbit interaction, and magnetic field, which inspires a promising route to enhance nonreciprocal response and its functionalities in spin orbitronics