The results of experimental studies of the magnetic and the superconducting properties of the compound Dy0.8Y0.2Rh4B4 with tetragonal body-centered crystal structure of the perovskite type (LuRu4B4) are presented. It is shown that the compound undergoes a paramagnet-ferrimagnet phase transition at the Curie temperature TC≈30.5K and its magnetic compensation temperature Tcomp≈17K. According to resistance measurements, the compound becomes a ferrimagnetic superconductor at Tconset≈5.9K which undergoes a ferrimagnet-antiferromagnet phase transition at TN≈2.7K while still remaining a superconductor. The specific heat exhibits a sharp maximum at this temperature. Point-contact Andreev reflection spectroscopy is used to measure the temperature and field dependences of the order parameter Δ(T,H) and the temperature dependence of the upper critical field Hc2(T). The dependences obtained differ radically from those generally accepted for conventional superconductors. The results obtained are discussed in connection with the possibility of triplet pairing in Dy0.8Y0.2Rh4B4.

The point-contact spectra of tantalum in the superconducting state, with T a, Cu, and Au counterelectrodes, have been studied. We discovered some new distinctive features, whose position on the eV axis is determined by the critical power required for the injection of nonequilibriumquasiparticles. At this level of power the band gap ∆ decreases abruptly in the vicinity of the contact. A correction to the point-contact spectrum, with the sign opposite to that of the usual correction, arises in the region of phonon energies. The maxima in the T a spectrum become sharper and their position on the energy axis becomes stabilized near the values eV ph = 7.0, 11.3, 15.5, and 18 meV , which correspond to low phonon group velocities ∂ω/∂q 0 in T a. This is confirmed by the existence of corresponding flattenings on the dispersion relations ω(q) of lattice vibrations. Slow phonons are created near the N −S interface in quasiparticle recombination and relaxation processes and cause a decrease in ∆ and an increase in the differential resistance in the vicinity of eV ph . An excess quasiparticle charge is accumulated in the region of the contact, producing a correction to the resistance, which decreases as eV , T , and H increase. These mechanisms are particularly effective in dirty contacts, thus permitting phonon spectroscopy in the superconducting state even when the current flow occurs in a nearly thermal mode.

The volt-ampere curves and their second derivatives were studied for niobium point contacts at low temperatures in the voltage range corresponding to the characteristic phonon energies. It was found that while for the dirty contacts in the normal state no PC spectra of phonons could be detected, in the superconducting state there were singularities in the I-V curves corresponding to maxima either in the first or in the second derivatives. The singularities observed were due to the energy dependence of the excess current. We suppose that the origin of these singularities is due to the inelastic transitions of electrons between chemical potentials of Cooper pairs at both sides of the contact, which differ in energy by $eV$. These transitions are possible if $\xi \left(0 \right)\gtrsim d \sim{{\Lambda}_{\varepsilon}}$ ($\xi (0)$ being the coherence length, $d$, the contact diameter, ${{\Lambda}_{\varepsilon}}={{({{l}_{i}}\cdot {{l}_{\varepsilon}})}^{1/2}}$, where ${{l}_{i}}$ and ${{l}_{\varepsilon}}$ being the elastic and inelastic electron mean free paths, respectively).Comment: 5 pages, 3 figure

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