576 research outputs found
Estimation of intraband and interband relative coupling constants from temperature dependences of the order parameter for two-gap superconductors
We present temperature dependences of the large and the small superconducting
gaps measured directly by SnS-Andreev spectroscopy in various Fe-based
superconductors and MgB. The experimental are well-fitted
with a two-gap model based on Moskalenko and Suhl system of equations
(supplemented with a BCS-integral renormalization). From the the fitting
procedure, we estimate the key attribute of superconducting state \textemdash
relative electron-boson coupling constants and eigen BCS-ratios for both
condensates. Our results evidence for a driving role of a strong intraband
coupling in the bands with the large gap, whereas interband coupling is rather
weak for all the superconductors under study.Comment: 7 pages, 5 figures, accepted to J. Supercond. Novel Mag
Hamiltonian formalism in Friedmann cosmology and its quantization
We propose a Hamiltonian formalism for a generalized
Friedmann-Roberson-Walker cosmology model in the presence of both a variable
equation of state (EOS) parameter and a variable cosmological constant
, where is the scale factor. This Hamiltonian system containing
1 degree of freedom and without constraint, gives Friedmann equations as the
equation of motion, which describes a mechanical system with a variable mass
object moving in a potential field. After an appropriate transformation of the
scale factor, this system can be further simplified to an object with constant
mass moving in an effective potential field. In this framework, the
cold dark matter model as the current standard model of cosmology corresponds
to a harmonic oscillator. We further generalize this formalism to take into
account the bulk viscosity and other cases. The Hamiltonian can be quantized
straightforwardly, but this is different from the approach of the
Wheeler-DeWitt equation in quantum cosmology.Comment: 7 pages, no figure; v2: matches the version accepted by PR
Evidence of a multiple boson emission in SmThOFeAs
We studied a reproducible fine structure observed in dynamic conductance
spectra of Andreev arrays in SmThOFeAs superconductors with various
thorium concentrations () and critical temperatures \,K. This structure is unambiguously caused by a multiple boson emission
(of the same energy) during the process of multiple Andreev reflections. The
directly determined energy of the bosonic mode reaches \,meV for optimal compound. Within the studied range of , this
energy as well as the large and the small superconducting
gaps, nearly scales with critical temperature with the characteristic ratio
(and ,
correspondingly) resembling the expected energy of spin
resonance and spectral density enhancement in and states,
respectively.Comment: 10 pages, 4 figure
Direct Evidence of Two Superconducting Gaps in FeSeTe: SnS-Andreev Spectroscopy and Lower Critical Field
We present direct measurements of the superconducting order parameter in
nearly optimal FeSeTe single crystals with critical temperature
K. Using intrinsic multiple Andreev reflection effect (IMARE)
spectroscopy and measurements of lower critical field, we directly determined
two superconducting gaps, meV and meV, and their temperature dependences. We show that a two-band
model fits well the experimental data. The estimated electron-boson coupling
constants indicate a strong intraband and a moderate interband interaction
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