2005

The whispering gallery mode dielectric resonator of a truncated cone shape was studied for the first time. The possibility of individual measuring the surface resistance of HTS films was shown experimentally in the millimeter wave band using resonators in the form of a cone and a hemisphere, which allows one to get rid of procedure with three pairs of films (<Barannik A.A., Bunyaev S.A., Cherpak N.T.).

It is shown that in the disk QDR a capillary filled with a lossy liquid, strong influence of liquid on the frequency of the field in the cavity is observed only at a certain layer thickness x, close to the value l_liq/4, which depends on the dielectric parameters of the test substances and determines the maximum diameter of a capillary d_max ~ 2x (Lavrinovich A.A.)

2006

A linear temperature dependence of the microwave conductivity of optimally doped HTSC YBa₂Cu₃O_7-d film was obtained at low temperatures (Barannik A.A., Cherpak N.T.).

2007

A new nonresonant radio-physical method for studying of complex conductivity of high-temperature superconductors was justified and developed. The developed method allows studying of high-temperature superconductors in extreme temperature conditions, which is essential to study the properties of high-temperature superconductors at the critical temperature and above it, i.e. in a normal state. The first results on the fluctuation conductivity investigation at a temperature from 115 K and below were obtained. The method may be useful for the study of other condensed matter, complex conductivity or permeability of which varies under the influence of external factors (Gubin A.I., Lavrinovich A.A, Cherpak N.T.)

2008

It was found that the residual surface resistance (i.e. resistance at T ®0) in superconductors YBa₂Cu₃O_7-d varies as a function of frequency ω^3/2 for films and single crystals, which suggests the intrinsic nature of this effect. These results were obtained using a new measurement technique of impedance properties investigation of high-Tc superconductors, proposed and developed by the authors on the basis of WGM sapphire resonators (Cherpak N.T., Barannik A.A., Bunyaev S.A.)

2009

The temperature dependence of the microwave surface resistance and surface reactance of new superconducting single crystal Ba (Fe1-xCox) 2As2 was obtained for the first time. These results were obtained using the proposed and developed by the authors technique of measuring impedance properties of new superconductors such as Fe-pnictides (Barannik A.A., Cherpak N.T., Torokhtii K.I.).

2010

The technique of processing the experimental results of measurement of the temperature dependence of the surface impedance of small sized superconductors by means of the WGM sapphire resonators was developed.The temperature dependence of the penetration depth, density of superconducting electronic component and density of quasi-particle component for a new superconducting single crystal Fe-pnictide, namely superconductor Ba (Fe_1-xCo_x)₂As₂ was obtained from the results of measurements in the millimeter wave band. The results show that the superconductor is not a BCS-type superconductor. According to the analysis of the temperature dependence of the penetration depth and the density of superconducting electronic component, symmetry of the order parameter can be s + / s- or nodal (nodal), that is, with the nodes of the gap function. Preliminary analysis of the temperature dependence of the quasi-particle liquid density shows no coherence peak, which does not coincide with those of other authors. This feature requires further investigation. The study of electromagnetic characteristics of sapphire QDR (i.e. WGM resonator) with HTS films as CEP and the radial gap with the measured superconducting sample inside of it was continued (Barannik A.A., Cherpak N.T.).

The theoretical analysis and simulation of the method of studying microwave response of HTS and related materials by measuring the reflectance of the sample during the propagation of the wave through the waveguide corner section with the sample under test were carried out at grazing angles of incidence. The expediency of using the corner section with smooth transitions, in which the height of the waveguide varies according to the hyperbolic tangent, was shown. The conditions for increasing the sensitivity of the method were determined and the optimal conditions were chosen based on the relationship between the height of the sample placing relative to  the waveguide, the angle of incidence and the linear dimensions of the test sample (Gubin A.I., Lavrinovich A.A.)

The HTS film-based transmission line of planar waveguide type with nonlinear properties was created. The characteristic power of the signal was found experimentally, at which the nonlinear dependence of the propagation of the input signal was observed. The ability to control non-linearity was demonstrated experimentally by passing DC through the line. (Gubin A.I., Lavrinovich A.A., Cherpak N.T.)

2011

1. A correlation between the quasiparticle scattering rate, the London depth and surface impedance for an arbitrary value of the mentioned rate in the Drude formula was generalized. The technique of the quasiparticle scattering rate determination in unconventional superconductors based on the experimental measurement results of the superconductors surface impedance dependending on temperature was elaborated. An estimation in a superconducting single crystal Ba (Fe_1-xCo_x)₂As₂ was obtained (Cherpak N.T., Barannik A.A.), The A modified coplanar waveguide transmission line based on epitaxial HTS film with nonlinear impedance was made jointly with the staff of Peter Gruenberg Institute, Forschungszentrum Juelich, Germany to continue studying peculiarities of such transmission lines with nonlinearity controlled by direct current (Gubin A.I., Lavrinovich A.A.)

2012

2. The relationshipbetween the effectiveand intrinsic(bulk) surface impedance was obtained for superconductingthin filmsunder condition when the microwave fieldat the surface ofthe filmhas an oppositedirectionrelative to the fieldat the oppositesurface of the film.The relationshipexpandsoptionsin thelocationof the thin filmin a microwave cavityandtherebyextends the capabilities ofthe studying superconductingthin films(Cherpak N.T.). The temperature dependence of the effective microwave impedance of the thin film superconducting FeSe_xTe_1–x was obtained experimentally. Other composites of this family of superconductors were studied abroad. The experimental data allow determining the main characteristics of the FeSe_xTe_1–x electronic system (Barannik A.A.). A mm-wave band stable oscillator based on a small-sized semiconductor module was created. The  analogues in Ukraine are absent. The oscillator was created to conduct studying of microwave properties of superconductors and bioliquids using WGM resonator technique developed in IRE NASU (Gubin A.I.) 

2013

On the basis of the microwave impedance measurements, the temperature dependence of the complex conductivity of superconducting chalcogenide FeSe_xTe_1-x was obtained and analyzed. The magnetic penetration depth exhibits a power-law behavior of, with an exponent n ≈ 2.4 at low temperatures, which corresponds to idea of s+/- symmetry of order parameter by analogy with pnictide BaFeCoAs where n=2.8. The first publication on microwave study of FeSe_xTe_1-x film was prepared. The results are important to clear up the basic properties of novel unconventional superconductors.

The step dependence of microwave loss on temperature was found during studying nonlinear peculiarities of HTS-based coplanar transmission line (waveguide). The width of a step feature depends on power of pulsed microwave field. Nature of the peculiarity has not cleared up and demands the further research.The obtained results can have practical importance for HTS-based microwave technology and be important to study nonlinear properties of superconductors in microwave fields.

A microwave characterization technique on the basis of a high-quality whispering-gallery mode (WGM) sapphire resonator with a microfluidic channel filled with the liquid under test was developed. The complex permittivity of aqueous solutions of proteins (cytochrome C, albumines) and glucose was measured depending on concentration with a high accuracy. The measurement technique is original. The results can be fundamental of a novel approach to dielectrometry of biological liquids on the whole and to dielectrometry of liquids of small volume specifically (Barannik A.A., Gubin A.I., Lavrinovich A.A.,Protsenko I.A., Kharchenko M.S., Cherpak N.T.).

2014

1. By continuingstudy of the nonlinear properties ofa coplanartransmission line (CPL) on the basis ofHTSCYBaCuOthin film, the authors found quenching transition to a stronglydissipative state of CPLby passing DC through it. An important feature ofthe observed effectis itsnon-destructivecharacter. In this case the superconducting propertiesare restored when thepower of the microwavesignal orDCvaluedecrease. The authors assumethat thenature of the effectmay be due toself-heatingHTSthinfilmstructurecaused bymagnetic flux flowwith an overalleffect of microwaveand DCcurrents.The effectmay havescientific significanceinthe field of nonlinearradio physics andapplied importancefor microwavetechnology(Gubin A.I., LavrinovichA.A.,CherpakN.T.).
2.  By developing microwave dielectrometry based on high-Q WGM resonators for study of lossy bioliquids with small volumes, the authors have developed an approach to solving the inverse electrodynamic problem under conditions when the Q-factor and frequency of the resonator depends on both the real and the imaginary part of permeability of liquid under test. The method can be of practical significance for the study and testing bioliquids of small volumes (Barannik A., Gubin A.I., Protsenko I.A.).
3.  The temperature dependence of the complex electron conductivity was obtained and the value of two energy gaps were found for chalcogenide superconductor The study was conducted for a thin (100 nm) epitaxial film. The results are qualitatively consistent with the results in the study of a single crystal FeSeTe by other authors, but there are significant differences that need to continue with the aim of consensus conclusions (Barannik A.A., Cherpak N.T.)