7 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
Depth-controlled beta-NMR of 8Li in a thin silver film.
Depth-controlled beta-NMR can be used to probe the magnetic properties of thin films and interfaces on a nanometer length scale. A 30 keV beam of highly spin-polarized 8Li+ ions was slowed down and implanted into a 50 nm film of Ag deposited on a SrTiO3 substrate. A novel high field beta-NMR spectrometer was used to observe two well resolved resonances which are attributed to Li occupying substitutional and octahedral interstitial sites in the Ag lattice. The temperature dependence of the Knight shifts and spin relaxation rates are consistent with the Korringa law for a simple metal, implying that the NMR of implanted 8Li reflects the spin suspectibility of bulk metallic silver
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 exo‐ and endothermic singlet fission rates by comparing the deuterated and parent chromophores. We find that changes in the frequency of the C−C deformation modes of Δω=6 cm−1 and the occurrence of C−D 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 electron–phonon coupling that drives the singlet fission process