11 research outputs found
Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn
We review the current status of Andreev reflection spectroscopy on the heavy
fermions, mostly focusing on the case of CeCoIn, a heavy-fermion
superconductor with a critical temperature of 2.3 K. This is a well-established
technique to investigate superconducting order parameters via measurements of
the differential conductance from nanoscale metallic junctions. Andreev
reflection is clearly observed in CeCoIn as in other heavy-fermion
superconductors. The measured Andreev signal is highly reduced to the order of
maximum 13% compared to the theoretically predicted value (100%).
Analysis of the conductance spectra using the extended BTK model provides a
qualitative measure for the superconducting order parameter symmetry, which is
determined to be -wave in CeCoIn. A phenomenological model is
proposed employing a Fano interference effect between two conductance channels
in order to explain both the conductance asymmetry and the reduced Andreev
signal. This model appears plausible not only because it provides good fits to
the data but also because it is highly likely that the electrical conduction
occurs via two channels, one into the heavy electron liquid and the other into
the conduction electron continuum. Further experimental and theoretical
investigations will shed new light on the mechanism of how the coherent
heavy-electron liquid emerges out of the Kondo lattice, a prototypical strongly
correlated electron system. Unresolved issues and future directions are also
discussed.Comment: Topical Review published in JPCM (see below), 28 pages, 9 figure
Visible-Light-Responsive Graphitic Carbon Nitride: Rational Design and Photocatalytic Applications for Water Treatment
Graphitic carbon nitride (g-C<sub>3</sub>N<sub>4</sub>) has recently
emerged as a promising visible-light-responsive polymeric photocatalyst;
however, a molecular-level understanding of material properties and
its application for water purification were underexplored. In this
study, we rationally designed nonmetal doped, supramolecule-based
g-C<sub>3</sub>N<sub>4</sub> with improved surface area and charge
separation. Density functional theory (DFT) simulations indicated
that carbon-doped g-C<sub>3</sub>N<sub>4</sub> showed a thermodynamically
stable structure, promoted charge separation, and had suitable energy
levels of conduction and valence bands for photocatalytic oxidation
compared to phosphorus-doped g-C<sub>3</sub>N<sub>4</sub>. The optimized
carbon-doped, supramolecule-based g-C<sub>3</sub>N<sub>4</sub> showed
a reaction rate enhancement of 2.3â10.5-fold for the degradation
of phenol and persistent organic micropollutants compared to that
of conventional, melamine-based g-C<sub>3</sub>N<sub>4</sub> in a
model buffer system under the irradiation of simulated visible sunlight.
Carbon-doping but not phosphorus-doping improved reactivity for contaminant
degradation in agreement with DFT simulation results. Selective contaminant
degradation was observed on g-C<sub>3</sub>N<sub>4</sub>, likely due
to differences in reactive oxygen species production and/or contaminant-photocatalyst
interfacial interactions on different g-C<sub>3</sub>N<sub>4</sub> samples. Moreover, g-C<sub>3</sub>N<sub>4</sub> is a robust photocatalyst
for contaminant degradation in raw natural water and (partially) treated
water and wastewater. In summary, DFT simulations are a viable tool
to predict photocatalyst properties and oxidation performance for
contaminant removal, and they guide the rational design, fabrication,
and implementation of visible-light-responsive g-C<sub>3</sub>N<sub>4</sub> for efficient, robust, and sustainable water treatment
Singlet Fission in Dideuterated Tetracene and Pentacene
AbstractThe impact of molecular vibrations on singlet fission, which is the spontaneous fission of a singlet exciton into two triplet excitons, is studied using ultrafast optical spectroscopy for the prototypical singlet fission chromophores tetracene and pentacene. We modify the frequency of intramolecular vibrations by deuteration, without impacting thin film structure and molecular arrangement, and study the resulting changes in exoâ and endothermic singlet fission rates by comparing the deuterated and parent chromophores. We find that changes in the frequency of the CâC deformation modes of ÎÏ=6â
cmâ1 and the occurrence of CâD vibrational modes do not lead to significant modifications in the singlet fission time constants. We conclude that the changes in the frequency of phonon modes induced by deuteration are too small to significantly impact the electronâphonon coupling that drives the singlet fission process