Josephson effect and Andreev reflection in Ba1–xNaxFe2As2 (x = 0.25 and 0.35) point contacts

III Международный семинар по микроконтактной спектроскопии<br>Харьков, Украина, 8–11 сентября 2014 г.

Анотація

I(V) characteristics and their first derivatives of ScS and ScN-type (S is superconductor, c is constriction, N is normal metal) point contacts (PCs) based on Ba_1–xNa_xFe₂As₂ (x = 0.25 and 0.35) were studied. ScS-type PCs with S = Nb,Ta, and Pb show Josephson-like resistively shunted I(V) curves with microwave induced Shapiro steps which satisfy relation 2eV = ћω. The I_cR_N product (I_c is critical current, R_N is normal state PC resistance) in these PCs is found to be up to 1.2 mV. All this data with the observed dependence of the I_c on the microwave power of ScS PCs with Pb counterelectrode indicates the presence of the singlet s-wave type pairing in Ba_1–xNa_xFe₂As₂. From the dV/dI(V) curves of ScN-type PCs demonstrating Andreev-reflection like features, the superconducting gap Δ ratio 2Δ/k_BT_c = 3.6 ± 1 for the compound with x = 0.35 was evaluated. Analysis of these dV/dI(V) at high biases V, that is well above Δ, testifies transition to the thermal regime in PCs with a voltage increase.