Group members:

 

Main areas of research

 

● Investigation of the thermodynamic parameters of high-temperature and magnetic superconductors.

 

● Study of the coexistence of superconductivity and magnetic ordering in the new high-temperature superconducting compounds.

 

● Investigation of the superconducting properties of magnetic superconductors, including by the method of Andreev reflection.

 

● Study of the ac and dc resistive properties of superconducting film structures.

 

● Study of the characteristics of the behavior of magnetoresistance in the latest materials.

 

 

Equipment

 

● Equipment for the influence of electromagnetic radiation with frequencies up to 100 GHz for superconductors at temperatures 2 - 4.2 K.

 

● Equipment for thin films deposition of metals in the oil-free vacuum ≈ 10 - 7  Mmhg.

 

● Equipment for the surface resistivity measuring in the temperature range 4.5 - 300 K and a frequency range 1 - 100 MHz.

 

● Equipment for the specific heat measuring  by vacuum adiabatic calorimeter in the temperature range 1.5 - 300 K.

 

● The point-contact spectrometer for investigation of nonlinear conductivity of contacts. Such spectrometer has a cryogenic equipment for formation of point contacts and measuring of their conducting properties in temperature interval 1.3 - 77 K, magnetic field range 0 - 3 T and under high-frequency irradiation in the range 0.3 - 65 GHz

 

 

Important results in recent years

 

• It is shown that the textured polycrystal Bi95.69Mn3.69Fe0.62 contains two phases — the bismuth matrix and inclusions of the α-BiMn phase. It is established that in the magnetic field the temperature dependences of the electrical resistivity behave nonmonotonically, and the magnetoresistance is positive in the entire temperature range and reaches a maximum value of 3033% in a magnetic field of 140 kOe for orientation, when the magnetic field is perpendicular to the transport current. It is assumed that the anomalous behavior of the temperature dependences of the electrical resistance in Bi95.69Mn3.69Fe0.62 and their discrepancy in comparison with pure bismuth is related to the influence of the magnetism of the α-BiMn phase and the external magnetic field on transport properties of this compound [1].

 

• We experimentally studied the effect of meter-range electromagnetic field (tens of MHz) on the current-voltage characteristic (I-V curve) of a wide superconducting film. The vortex resistivity region is shown to significantly extend under the effect of meter-range (MR) electromagnetic irradiation owing to rapid suppression of critical current with a slower change in the upper boundary of stability of the vortex state. We found that as the MR irradiation power increases, the I-V curve structure related to phase slip lines is smoothed out to eventually vanish [2].

 

• It was established that in the magnetic superconductor Dy0.6Y0.4Rh3.85Ru0.15B4 at the temperature TFM = (21 ± 1) K a transition to the ferromagnetic state takes place and at Тc = (6.7 ± 1) K a transition to the superconducting state is observed, which coexists with the ferromagnetic phase in a wide temperature range of 2–6.7 K. It is suggested that a triplet mechanism of superconducting pairing is possible presented for Dy0.6Y0.4Rh3.85Ru0.15B4 [3].

 

• For the first time, peculiarities in the temperature dependences of electrical resistivity ρ(T) (maximum and minimum for Gd0.9Pb0.1Mo6S8 and inflection point for Gd0.7Pb0.3Mo6S8) in compounds Gd0.9Pb0.1Mo6S8 and Gd0.7Pb0.3Mo6S8 were revealed. The presence of a small positive magnetoresistance (up to 2 %), which is maximum at the temperature of the features, has been established. It is shown that the dependence M(T) in the studied temperature range, there are no features associated with long range magnetic transformations. It has been suggested that the features on ρ(Т) in Gd0.9Pb0.1Mo6S8 and Gd0.7Pb0.3Mo6S8 can be due to the restructuring of the band structure and the appearance of two charge carrier channels responsible for the semiconductor and metal behavior of the electrical resistance temperature dependences [4].

 

• It is shown that the superconducting transition temperature values Tc in the magnetic superconductors GdxPb1–xMo6S8  decrease  from 14.6 K for a compound with x = 0.5 to 11.8 K for x = 0. Experimental dependences Hc2(T) were plotted and it was found that the theoretical dependence Hc2(T) within the microscopic theory of Werthamer–Helfand–Hohenberg poorly describes the experimental data for the Gd0.9Pb0.1Mo6S8 compound. At the same time, the fit of Hc2(T) within the Ginzburg–Landau theory is in good agreement with the experimental results for all the studied samples. An explanation of the dependence Hc2(T) of the studied samples from the gadolinium concentration was proposed. Using to microcontact spectroscopy of Andriiv reflection for the Gd0.5Pb0.5Mo6S8–Ag heterocontact, the size of the superconducting gap was estimated (Δ ≈ 1.95 meV at 2.6 K). The resulting ratio was 2Δ/kBTc ≈ 3.02, which is lower than the Bardeen– Cooper–Schrieffer value of 3.52 for conventional weakly coupled superconductors [5].