8,563 research outputs found
Theory of interfacial charge-transfer complex photophysics in -conjugated polymer-fullerene blends
We present a theory of the electronic structure and photophysics of 1:1
blends of derivatives of polyparaphenylenevinylene and fullerenes. Within the
same Coulomb-correlated Hamiltonian applied previously to interacting chains of
single-component -conjugated polymers, we find an exciplex state that
occurs below the polymer's optical exciton. Weak absorption from the ground
state occurs to the exciplex. We explain transient photoinduced absorptions in
the blend, observed for both above-gap and below-gap photoexcitations, within
our theory. Photoinduced absorptions for above-gap photoexcitation are from the
optical exciton as well as the exciplex, while for below-gap photoexcitation
induced absorptions are from the exciplex alone. In neither case are free
polarons generated in the time scale of the experiment. Importantly, the
photophysics of films of single-component -conjugated polymers and blends
can both be understood by extending Mulliken's theory of ground-state charge
transfer to the case of excited-state charge transfer.Comment: 9 pages, 8 figure
Controlling quantum transport through a single molecule
We investigate multi-terminal quantum transport through single monocyclic
aromatic annulene molecules, and their derivatives, using the nonequilibrium
Green function approach in the self-consistent Hartree-Fock approximation. A
new device concept, the Quantum Interference Effect Transistor (QuIET) is
proposed, exploiting perfect destructive interference stemming from molecular
symmetry, and controlling current flow by introducing decoherence and/or
elastic scattering that break the symmetry. This approach overcomes the
fundamental problems of power dissipation and environmental sensitivity that
beset many nanoscale device proposals.Comment: 4 pages, 5 figure
The ubiquitous 1100 charge ordering in organic charge-transfer solids
Charge and spin-orderings in the 1/4-filled organic CT solids are of strong
interest, especially in view of their possible relations to organic
superconductivity. We show that the charge order (CO) in both 1D and 2D CT
solids is of the ...1100... type, in contradiction to mean field prediction of
>...1010... CO. We present detailed computations for metal-insulator and
magnetic insulator-insulator transitions in the theta-ET materials. Complete
agreement with experiments in several theta systems is found. Similar
comparisons between theory and experiments in TCNQ, TMTTF, TMTSF, and ET
materials prove the ubiquity of this phenomenon.Comment: 3 pages, 4 eps figures; ICSM 200
A new study on the emission of EM waves from large EAS
A method used in locating the core of individual cosmic ray showers is described. Using a microprocessor-based detecting system, the density distribution and hence, energy of each detected shower was estimated
Oscillating magnetoresistance due to fragile spin structure in metallic GdPd
Studies on the phenomenon of magnetoresistance (MR) have produced intriguing
and application-oriented outcomes for decades--colossal MR, giant MR and
recently discovered extremely large MR of millions of percents in semimetals
can be taken as examples. We report here the investigation of oscillating MR in
a cubic intermetallic compound GdPd, which is the only compound that
exhibits MR oscillations between positive and negative values. Our study shows
that a very strong correlation between magnetic, electrical and
magnetotransport properties is present in this compound. The magnetic structure
in GdPd is highly fragile since applied magnetic fields of moderate
strength significantly alter the spin arrangement within the system--a behavior
that manifests itself in the oscillating MR. Intriguing magnetotransport
characteristics of GdPd are appealing for field-sensitive device
applications, especially if the MR oscillation could materialize at higher
temperature by manipulating the magnetic interaction through perturbations
caused by chemical substitutions.Comment: 10 pages, 7 figures. A slightly modified version is published in
Scientific Report
Microprocessor-based single particle calibration of scintillation counter
A microprocessor-base set-up is fabricated and tested for the single particle calibration of the plastic scintillator. The single particle response of the scintillator is digitized by an A/D converter, and a 8085 A based microprocessor stores the pulse heights. The digitized information is printed. Facilities for CRT display and cassette storing and recalling are also made available
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