1,645 research outputs found
Ultrafast Acousto-Plasmonics in Gold Nanoparticles Superlattice
We report the investigation of the generation and detection of GHz coherent
acoustic phonons in plasmonic gold nanoparticles superlattices (NPS). The
experiments have been performed from an optical femtosecond pump-probe scheme
across the optical plasmon resonance of the superlattice. Our experiments allow
to estimate the collective elastic response (sound velocity) of the NPS as well
as an estimate of the nano-contact elastic stiffness. It appears that the
light-induced coherent acoustic phonon pulse has a typical in-depth spatial
extension of about 45 nm which is roughly 4 times the optical skin depth in
gold. The modeling of the transient optical reflectivity indicates that the
mechanism of phonon generation is achieved through ultrafast heating of the NPS
assisted by light excitation of the volume plasmon. These results demonstrate
how it is possible to map the photon-electron-phonon interaction in
subwavelength nanostructures
Thermally activated intersubband scattering and oscillating magnetoresistance in quantum wells
Experimental studies of magnetoresistance in high-mobility wide quantum wells
reveal oscillations which appear with an increase in temperature to 10 K and
whose period is close to that of Shubnikov-de Haas oscillations. The observed
phenomenon is identified as magnetointersubband oscillations caused by the
scattering of electrons between two occupied subbands and the third subband
which becomes occupied as a result of thermal activation. These small-period
oscillations are less sensitive to thermal suppression than the largeperiod
magnetointersubband oscillations caused by the scattering between the first and
the second subbands. Theoretical study, based on consideration of electron
scattering near the edge of the third subband, gives a reasonable explanation
of our experimental findings.Comment: 9 pages, 5 figure
Microwave zero-resistance states in a bilayer electron system
Magnetotransport measurements on a high-mobility electron bilayer system
formed in a wide GaAs quantum well reveal vanishing dissipative resistance
under continuous microwave irradiation. Profound zero-resistance states (ZRS)
appear even in the presence of additional intersubband scattering of electrons.
We study the dependence of photoresistance on frequency, microwave power. and
temperature. Experimental results are compared with a theory demonstrating that
the conditions for absolute negative resistivity correlate with the appearance
of ZRS.Comment: 5 pages, 4 figure
High order fractional microwave induced resistance oscillations in 2D systems
We report on the observation of microwave-induced resistance oscillations
associated with the fractional ratio n/m of the microwave irradiation frequency
to the cyclotron frequency for m up to 8 in a two-dimensional electron system
with high electron density. The features are quenched at high microwave
frequencies independent of the fractional order m. We analyze temperature,
power, and frequency dependencies of the magnetoresistance oscillations and
discuss them in connection with existing theories.Comment: 5 pages, 5 figure
Non-linear transport phenomena in a two-subband system
We study non-linear transport phenomena in a high-mobility bilayer system
with two closely spaced populated electronic subbands in a perpendicular
magnetic field. For a moderate direct current excitation, we observe
zero-differential-resistance states with a characteristic 1/B periodicity. We
investigate, both experimentally and theoretically, the Hall field-induced
resistance oscillations which modulate the high-frequency magneto-intersubband
oscillations in our system if we increase the current. We also observe and
describe the influence of direct current on the magnetoresistance in the
presence of microwave irradiation.Comment: 8 pages, 6 figure
Microscopic Evidence of Spin State Order and Spin State Phase Separation in Layered Cobaltites RBaCo2O5.5 with R=Y, Tb, Dy, and Ho
We report muon spin relaxation measurements on the magnetic structures of
RBaCo_2O_5.5 with R=Y, Tb, Dy, and Ho. Three different phases, one
ferrimagnetic and two antiferromagnetic, are identified below 300 K. They
consist of different ordered spin state arrangements of high-, intermediate-,
and low-spin Co^3+ of CoO_6 octahedra. Phase separation into well separated
regions with different spin state order is observed in the antiferromagnetic
phases. The unusual strongly anisotropic magnetoresistance and its onset at the
FM-AFM phase boundary is explained.Comment: 4 pages, accepted for publication in Phys. Rev. Let
Acoustic Probing of the Jamming Transition in an Unconsolidated Granular Medium
Experiments with acoustic waves guided along the mechanically free surface of
an unconsolidated granular packed structure provide information on the
elasticity of granular media at very low pressures that are naturally
controlled by the gravitational acceleration and the depth beneath the surface.
Comparison of the determined dispersion relations for guided surface acoustic
modes with a theoretical model reveals the dependencies of the elastic moduli
of the granular medium on pressure. The experiments confirm recent theoretical
predictions that relaxation of the disordered granular packing through
non-affine motion leads to a peculiar scaling of shear rigidity with pressure
near the jamming transition corresponding to zero pressure. Unexpectedly, and
in disagreement with the most of the available theories, the bulk modulus
depends on pressure in a very similar way to the shear modulus
Microwave-induced Hall resistance in bilayer electron systems
The influence of microwave irradiation on dissipative and Hall resistance in
high-quality bilayer electron systems is investigated experimentally. We
observe a deviation from odd symmetry under magnetic field reversal in the
microwave-induced Hall resistance whereas the dissipative
resistance obeys even symmetry. Studies of as a
function of the microwave electric field and polarization exhibit a strong and
non-trivial power and polarization dependence. The obtained results are
discussed in connection to existing theoretical models of microwave-induced
photoconductivity.Comment: 8 pages, 5 figure
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