108 research outputs found
Optically Controlled Excitonic Transistor
Optical control of exciton fluxes is realized for indirect excitons in a
crossed-ramp excitonic device. The device demonstrates experimental proof of
principle for all-optical excitonic transistors with a high ratio between the
excitonic signal at the optical drain and the excitonic signal due to the
optical gate. The device also demonstrates experimental proof of principle for
all-optical excitonic routers
Freezing of spin and charge in La_(2-x)Sr_xCuO_4
Zero- and longitudinal-field muon-spin relaxation Ό+SR measurements have been performed on La_(2-x)Sr_xCuO_4 alloys in both single-crystal and sintered powder forms above and below their magnetic transition temperatures, T_f. The Ό+ precession frequency v depends only weakly on x and T_f, an observation which together with resistivity data implies classical freezing of magnetic moments in the regime where the carriers are localized. For x=0.05, critical dynamics are observed near T_f. The Ό^+SR technique is shown to be very sensitive to ferromagnetically aligned pairs of Cu^(2+) moments; the population of such pairs increases greatly with x
Concentration Dependence of Superconductivity and Order-Disorder Transition in the Hexagonal Rubidium Tungsten Bronze RbxWO3. Interfacial and bulk properties
We revisited the problem of the stability of the superconducting state in
RbxWO3 and identified the main causes of the contradictory data previously
published. We have shown that the ordering of the Rb vacancies in the
nonstoichiometric compounds have a major detrimental effect on the
superconducting temperature Tc.The order-disorder transition is first order
only near x = 0.25, where it cannot be quenched effectively and Tc is reduced
below 1K. We found that the high Tc's which were sometimes deduced from
resistivity measurements, and attributed to compounds with .25 < x < .30, are
to be ascribed to interfacial superconductivity which generates spectacular
non-linear effects. We also clarified the effect of acid etching and set more
precisely the low-rubidium-content boundary of the hexagonal phase.This work
makes clear that Tc would increase continuously (from 2 K to 5.5 K) as we
approach this boundary (x = 0.20), if no ordering would take place - as its is
approximately the case in CsxWO3. This behaviour is reminiscent of the
tetragonal tungsten bronze NaxWO3 and asks the same question : what mechanism
is responsible for this large increase of Tc despite the considerable
associated reduction of the electron density of state ? By reviewing the other
available data on these bronzes we conclude that the theoretical models which
are able to answer this question are probably those where the instability of
the lattice plays a major role and, particularly, the model which call upon
local structural excitations (LSE), associated with the missing alkali atoms.Comment: To be published in Physical Review
Unusual kondo behavior in the indium-rich heavy fermion antiferromagnet Ce3Pt4In13
We report the thermodynamic, magnetic, and electronic transport properties of
the new ternary intermetallic system (Ce,La)3Pt4In13. Ce3Pt4In13 orders
antiferromagnetically at 0.95 K while the non-magnetic compound La3Pt4In13 is a
conventional 3.3 K superconductor. Kondo lattice effects appear to limit the
entropy associated with the Neel transition to (1/4)Rln2 as an electronic
contribution to the specific heat of gamma = 1 J/mole-Ce K2 is observed at TN;
roughly 35% of this gamma survives the ordering transition. Hall effect,
thermoelectric power, and ambient-pressure resistivity measurements confirm
this interpretation. These results suggest that RKKY and Kondo interactions are
closely balanced in this compound (TN = TK). Contrary to expectations based on
the Doniach Kondo necklace model, applied hydrostatic pressure modestly
enhances the magnetic ordering temperature with dTN/dP = +23 mK/kbar. As such
Ce3Pt4In13 provides a counterexample to Kondo systems with similar Kondo and
RKKY energy scales wherein applied pressure enhances TK at the expense of the
ordered magnetic state.Comment: submitted to Physical Review
High-pressure decomposition of synthetic garnets
The stability of synthetic garnets {Y3}[Fe2](Fe3)O12, {Y3}[Al2](Al3)O12, and {Y3}[Ga2](Ga3)O12 has been investigated at high pressures and high temperatures. Decomposition to the YXO3 compound (X=Fe or Al) with the perovskitelike structure and to the sesquioxide with the corundum structure has been found to occur in the former two garnets: {Y3}[X2](X3)O12â3 YXO3+X2O3, while in the case of yttriumâgallium garnet no breakdown was detected at pressures up to 44 kbar and 1000°C. The three garnets seem to behave differently at high pressure and high temperature. This appears to be related to the differences in the preference of the three cations for the tetrahedral site. Results of preliminary studies of the effect of high pressure and high temperature on Li0.5Fe2.5O4 are presented.
The geophysical implications of the decomposition under high pressure and high temperature of the garnet structure are discussed
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