33 research outputs found
Single 20meV boson mode in KFe2As2 detected by point-contact spectroscopy
We report an experimental and theoretical investigation of the electron-boson
interaction in KFe2As2 by point-contact (PC) spectroscopy, model, and ab-initio
LDA-based calculations for the standard electron-phonon Eliashberg function.
The PC spectrum viz. the second derivative of the I - V characteristic of
representative PC exhibits a pronounced maximum at about 20meV and surprisingly
a featureless behavior at lower and higher energies. We discuss phonon and
non-phonon (excitonic) mechanisms for the origin of this peak. Analysis of the
underlying source of this peak may be important for the understanding of
serious puzzles of superconductivity in this type of compounds.Comment: 10 pages, 6 figs., to be published in PR
The superconducting gaps in FeSe studied by soft point-contact Andreev reflection spectroscopy
FeSe single crystals have been studied by soft point-contact
Andreev-reflection spectroscopy. Superconducting gap features in the
differential resistance dV/dI(V) of point contacts such as a characteristic
Andreev-reflection double-minimum structure have been measured versus
temperature and magnetic field. Analyzing dV/dI within the extended two-gap
Blonder-Tinkham-Klapwijk model allows to extract both the temperature and
magnetic field dependence of the superconducting gaps. The temperature
dependence of both gaps is close to the standard BCS behavior. Remarkably, the
magnitude of the double-minimum structure gradually vanishes in magnetic field,
while the minima position only slightly shifts with field indicating a weak
decrease of the superconducting gaps. Analyzing the dV/dI(V) spectra for 25
point contacts results in the averaged gap values = 1.8+/-0.4meV and
=1.0+/-0.2 meV and reduced values 2/kTc=4.2+/-0.9 and
2/kTc=2.3+/-0.5 for the large (L) and small (S) gap, respectively.
Additionally, the small gap contribution was found to be within tens of percent
decreasing with both temperature and magnetic field. No signatures in the dV/dI
spectra were observed testifying a gapless superconductivity or presence of
even smaller gaps.Comment: 8 pages, 4 figs., 3 tables. Shortened version without fig.4 and Table
3 is accepted for publication in Phys. Rev.