Exploring point-contact spectra of Ba1−xNaxFe2As2 in the normal and superconducting states
Yu. G. Naidyuk, O. E. Kvitnitskaya, S. Aswartham, G. Fuchs, K. Nenkov, S. Wurmehl
DOI 10.1103/PhysRevB.89.104512 · Physical Review B
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Abstract
We present a study of the derivatives of current-voltage I(V) characteristics of point contacts (PCs) based on Ba1−xNaxFe2As2 (x=0.25) in the normal and superconducting states. The detailed analysis of dV/dI(V) data (also given in Appendix A) shows that the thermal regime, when the temperature increases with voltage at a rate of about 1.8 K/mV, is realized in the investigated PCs at least at high biases V above the superconducting (SC) gap Δ. In this case, the specific resistivity ρ(T) in the PC core is responsible for a peculiar dV/dI(V) behavior, while a pronounced asymmetry of dV/dI(V) is caused by the large value of thermopower in this material. A reproducible minima detected in dV/dI(V) at low biases in the range ±(6–9) mV, well below the SC critical temperature Tc, could be connected with the manifestation of the SC gap Δ. An evaluation of these Andreev-reflection-like structures on dV/dI(V) points out to the preferred value of 2Δ/kBTc≈6. The expected second gap features in dV/dI(V) are hard to resolve unambiguously, likely due to impurity scattering, spatial inhomogeneity, and transition to the mentioned thermal regime as the bias further increases. Suggestions are made how to separate the spectroscopic features in dV/dI(V) from those caused by the thermal regime.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Ba1-xNaxFe2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 34 | Pressure not reported | unknown |
| Ba0.75Na0.25Fe2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 10 | Pressure not reported | onset |
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