ИСТИНА

A detailed investigation of multiband superconductivity and low-frequency Leggett's plasma resonances [1] in Mg1-xAlxB2 system (0 < x < 0.4) was carried out with a help of Josephson and multiple Andreev reflections effect (MARE) spectroscopy of individual ScS [2] Sharvin-type contacts. Two distinct bulk superconducting gaps was obtained: deltaL = (11 ± 1) meV, deltas = (2 ± 0.5) meV (critical temperature Тс ~ 41 K). In the range of 12 K < Тс < 41 K has been found that amplitude of the large gap deltaL scales by Тс. BCS-ratio 2deltaL/kBTc = 6 ± 1 points out quasi-2D superconductivity in Mg1-xAlxB2. In the range of Тс > 15 K the small gap deltas does not depend on Тс, at Тс < 15 K the s-gap starts to close. A fine structure corresponding to the low frequency plasma modes was observed on CVC of Josephson (SIS) and Andreev (SnS) Mg1-xAlxB2 - contacts and investigated [3]. It was found that energy value of Leggett plasma mode omega0 ~ (4 - 5) meV (at T = 4.2 K, local Tc > 30 K) and (omega0)^2 is proportional to the (deltaL*deltas) [3]. These facts are in good agreement with the theoretical predictions [4,5,6]