B. Verkin Institute for Low Temperature Physics and Engineering National Academy of Science (NAS) of Ukraine
DEPARTMENT OF POINT-CONTACT SPECTROSCOPY
Head of the Department
Projects and Grants
Main web-page of ILTPE
Investigation of the thermal (heat capacity), superconducting, ac and dc resistive properties of the modern superconducting structures
The Wohlleben effect (the positive response in the superconducting state while measuring the temperature dependence of magnetization in the FC mode) was detected in Dy1-xYxRh4B4 compounds. It was shown that the effect exists in both magnetic Dy1-xYxRh4B4 (x = 0.2, 0.3, 0.4, 0.6) and nonmagnetic YRh4B4 superconductors.
The investigation of the magnetic properties of Dy1-xYxRh4B4 compound shows that the phase transition at T~30K is a paramagnet-ferrimagnet transition. It is shown that ferrimagnetism also persists be low the temperature of superconducting ordering. As follows from the heat capacity data, there occurs another phase transformation several degrees below the temperature of the superconducting transition, which is most likely magnetic and related to the ferrimagnet – antiferromagnet transition. It is found that the phase transition has a significant effect on the charge subsystem of the superconductor and the parameter Δ.
The magnetic properties and the electric transport of a new magnetic HTSC compound EuÀsFeO0.85F0.15 have been investigated. The first (Íc1) and the second (Íc2 ) critical magnetic fields as well as the corresponding magnetic penetration depths λ and coherence lengths have been estimated near Tc. Starting with the lowest fields the temperature dependence Íc2(Ò) exhibits a pronounced hyperbolic behavior. The Andreev reflection spectra have been measured in point contacts based on this compound, which shows the presence of both one-gap and two- gap spectra. Most of the spectra show features that correspond to the case of two – gaps with magnitudes 2Δs/kÒñ = 2.2 – 4.7 è 2Δ1/kÒñ = 5,1 – 11,7. The anomalously high parameters 2Δ/kÒñ are indicative of a unconventional mechanism of pairing. These findings and the absence of zero gaps in the all measured spectra give evidence in favor of the anisotropic s-wave (or s±) symmetry of the order parameter in the investigated compound.
Equipment for the influence of electromagnetic radiation with frequencies up to
100 GHz for superconductors at temperatures 2 - 4.2 K.
3. Equipment for the surface resistivity measuring in the temperature range 4.5 - 300 K and a frequency range 1 - 100 MHz.
4. Equipment for the specific heat measuring by vacuum adiabatic calorimeter in the temperature range 1.5 - 300 K.
5. 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.
1. Zolochevskii I. V. Resistive states in wide superconducting films induced by dc and ac currents (review ) // Low Temp. Phys., 40, ¹ 10, 867 - 892 (2014).
2. Zolochevskii I. V. Stimulation of superconductivity by microwave irradiation in wide tin films (review ) // Low Temp. Phys., 39, ¹ 7, 571-585 (2013).
3. Dmitriev V.M., Terekhov A.V., Zaleski A., Khatsko E.N., Kalinin P.S., Rykova A.I., Gurevich A.M., Glagolev S.A., Khlybov E.P., Kostyleva I.E., and Lachenkov S.A. The Wohlleben effect in magnetic superconductors Dy1-xYxRh4B4 (x = 0.2, 0.3, 0.4 and 0.6) // Low Temp. Phys., 38, ¹ 2, 154 (2012).
4. Terekhov A.V. Wohlleben effect in YRh4B4 // Low Temp. Phys., 39, ¹ 7, 640 (2013).
5. Dmitriev V.M., Khlybov E.P., Kondrashov D.S., Terekhov A.V., Rybaltchenko L.F., Khristenko E.V., Ishchenko L.A., Kostyleva I.E. and Zaleski A.J. Andreev reflection spectroscopy of the new Fe-based superconductor EuAsFeO(0.85)F(0.15): evidence for the strong order parameter anisotropy // Low Temp. Phys., 37, ¹ 4, 280 (2011).
6. Dmitriev V.M., Zaleski A., Khlybov E.P., Rybaltchenko L.F., Khristenko E.V., Ishchenko L.A., and Terekhov A.V. Enhancement of superconducting order parameter in the compound Dy0.8Y0.2Rh4B4 at the phase transition of its magnetic subsystem from antiferromagnetic to ferrimagnetic state // Low Temp. Phys., 35, ¹ 5, 424 (2009).
7. Dmitriev V.M., Zaleski A.J., Khlybov E.P.,
Rybaltchenko L.F., Khristenko E.V., Ishchenko L.A., Terekhov A.V., Kostyleva
I.E., and Lachenkov S.A. Magnetic phase transformations and superconductivity in
Low Temp. Phys., 34, ¹ 11, 909 (2008).