44,065 research outputs found
Unusual Tunneling Characteristics of Double-quantum-well Heterostructures
We report tunneling phenomena in double InGaAs quantum-well
structures that are at odds with the conventional parallel-momentum-conserving
picture of tunneling between two-dimensional systems. We found that the
tunneling current was mostly determined by the correlation between the emitter
and the state in one well, and not by that between those in both wells. Clear
magnetic-field-dependent features were first observed before the main
resonance, corresponding to tunneling channels into the Landau levels of the
well near the emitter. These facts provide evidence of the violation of
in-plane momentum conservation in two-dimensional systems.Comment: Submitted to ICPS-27 conference proceeding as a contributed pape
Structural and Correlation Effects in the Itinerant Insulating Antiferromagnetic Perovskite NaOsO3
The orthorhombic perovskite NaOsO3 undergoes a continuous metal-insulator
transition (MIT), accompanied by antiferromagnetic (AFM) order at T_N=410 K,
suggested to be an example of the rare Slater (itinerant) MIT. We study this
system using ab initio and related methods, focusing on the origin and nature
of magnetic ordering and the MIT. The rotation and tilting of OsO6 octahedra in
the GdFeO3 structure result in moderate narrowing the band width of the t_{2g}
manifold, but sufficient to induce flattening of bands and AFM order within the
local spin density approximation (LSDA), where it remains metallic but with a
deep pseudogap. Including on-site Coulomb repulsion U, at U_c ~2 eV a MIT
occurs only in the AFM state. Effects of spin-orbit coupling (SOC) on the band
structure seem minor as expected for a half-filled shell, but SOC
doubles the critical value U_c necessary to open a gap and also leads to large
magnetocrystalline energy differences in spite of normal orbital moments no
greater than 0.1. Our results are consistent with a Slater MIT driven by
magnetic order, induced by a combination of structurally-induced band narrowing
and moderate Coulomb repulsion, with SOC necessary for a full picture. Strong
p-d hybridization reduces the moment, and when bootstrapped by the reduced
Hund's rule coupling (proportional to the moment) gives a calculated moment of
~1 , consistent with the observed moment and only a third of the formal
value. We raise and discuss one important question: since this AFM
ordering is at q=0 (in the 20 atom cell) where nesting is a moot issue, what is
the microscopic driving force for ordering and the accompanying MIT?Comment: 9 page
Drastic Reduction of Shot Noise in Semiconductor Superlattices
We have found experimentally that the shot noise of the tunneling current
through an undoped semiconductor superlattice is reduced with respect to the
Poissonian noise value , and that the noise approaches 1/3 of that value
in superlattices whose quantum wells are strongly coupled. On the other hand,
when the coupling is weak or when a strong electric field is applied to the
superlattice the noise becomes Poissonian. Although our results are
qualitatively consistent with existing theories for one-dimensional mulitple
barriers, the theories cannot account for the dependence of the noise on
superlattice parameters that we have observed.Comment: 4 Pages, 3Figure
Zeta Potential of Modified Multi-walled Carbon Nanotubes in Presence of poly (vinyl alcohol) Hydrogel
The main objective of this study is investigate the behavior of the Zeta Potential of the MWCNT modified with SDS(Sodium Dodecyl Sulfate) and CTAB(Cetyl Tetraethyl Ammonium Bromide) in presence of PVA. Full hydrolyzed PVA was used. As a result, adding PVA in the CNT solution led to decrease the Zeta Potential. The Zeta Potential of suspended colloid varied from 42.00mV to 6.48mV and -45.00mV to -6.4mV at 1.5% concentration of PVA; according with the changing pH, the Zeta Potential dropped to near zero at pH 3 and 11. The pH and PVA has strong influence in the reduction of ZP of MWCNT solution. MWCNT-PVA solution with 33.30mV, -35.69mV at 0.01% of PVA was exposed under AC field; a uniform coat was obtained, with the SDS-MWCNT-PVA solution.National Natural Science Foundation of China Project (Grant No.51073024), the Royal Society-NSFC international joint project (Grant No.51111130207) and Beijing Municipal Science and Technology Plan Projects (No. Z111103066611005)
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