B. Verkin Institute for Low Temperature Physics and Engineering National Academy of Science (NAS) of Ukraine


Head of the Department  
Prof. Naidyuk Yurii Georgievich
Tel : +(380)-57-3402211, Fax: +(380)-57-3403370, +(380)-57-3450593, e-mail: naidyuk at ilt.kharkov.ua


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Andreev-reflection and PC spectroscopy of modern superconductors


Bashlakov D.L. bashlakov at ilt.kharkov.ua 
Bobrov N.L. bobrov at ilt.kharkov.ua 
Gamayunova N.V. gamayunova at ilt.kharkov.ua 
Kvitnitskaya О.Е. kvitnitskaya at ilt.kharkov.ua 
Naidyuk Yu.G. naidyuk at ilt.kharkov.ua 
Tiutrina L.V. tiutrina at ilt.kharkov.ua 


Main research:

  • investigation of modern superconductors — rare-earth nickelborocarbides, magnesium diboride, high-temperature and iron-based superconductors by Andreev reflection spectroscopy;

  • obtaining of point-contact spectra of electron-quasiparticle interaction for above mentioned materials;

  • investigation of coexistence of superconductivity, magnetic ordering and spin/charge density waves in new high-temperature superconducting compounds.

Main recent results:


The data on the distribution of superconducting gap in new superconductor MgB2 with the critical temperature of 39 К were obtainedThe presence of two gaps in MgB2 is established. Their values are found to be 2,45±0,15 and 7,0±0.4 mV with the relation 1:3, what is in accordance with the theoretical estimations.
The existence of two superconducting gaps in non-magnetic R=Y, Lu and antiferromagnetic FМ) R=Tm, Er nickel-borocarbide superconducting compounds RNi2B2C was shown. The superconducting gap for compounds with commensurate АFM order R=Ho and Dy has a BCS-like behavior in the antiferromagnetic state. The gap for R=Tm starts to decrease at the approach to the magnetic state with non-commensurate АFМ order.

The existence of two-band superconducting state for antiferromagnetic (TN=6K) nickel-borocarbide superconductor (Tc =11.3K) ErNi2B2C is shown. Such state is characterized by two order-parameters. The temperature dependence of order parameter along two main crystallographic directions was obtained. The essential decrease of superconducting order parameter at the transition in the antiferromagnetic state was revealed.

Using point-contact Andreev-reflection spectroscopy, emergent iron-based pnictide and chalcogenide superconductors of different structure have been investigated. Along with determination of superconducting gap and its temperature and magnetic field dependence suggestions was made how to separate the spectroscopic features in dV/dI(V) from those caused by the thermal regime. Using Yanson point-contact spectroscopy single 20 meV boson mode in KFe2As2 was detected. A rise in the superconducting critical temperature Tc of more than two times (exceeding 20 K) is discovered in point contacts created between iron chalcogenide FeSe single crystals and Cu.




The point-contact spectrometers for investigation of nonlinear conductivity of point contacts. The spectrometers have a cryogenic equipment for creation of point contacts and measuring of
conducting properties of point contacts in temperature interval 1.5-77 K and magnetic field 0-9T.

International collaboration:

- Institute of Experimental Physics, Kosice, Slovak Republik

- Leibniz Institute for Solid State and Materials Research, Dresden, Germany

- Physical Institute University of Karlsruhe, Karlsruhe, Germany

- Texas A&M University, College Station, USA

Recent publications and reviews:

  1. Yu. G. Naidyuk, O. E. Kvitnitskaya, N. V. Gamayunova D. L. Bashlakov, L. V. Tyutrina, G. Fuchs, R. Hühne, D. A. Chareev, and A. N. Vasiliev, Superconducting gaps in FeSe studied by soft point-contact Andreev reflection spectroscopy,  Phys. Rev. B 96, 094517 (2017)

  2. Yu.G. Naidyuk, G. Fuchs, D.A. Chareev, A.N. Vasiliev, Doubling of the critical temperature of FeSe observed in point contacts,  Phys. Rev. B 93, 144515 (2016).

  3. Yu. G. Naidyuk, O.E. Kvitnitskaya, S. Aswartham, G. Fuchs, K. Nenkov, and S. Wurmehl, Exploring point-contact spectra of Ba1−xNaxFe2As2 in the normal and superconducting states, Phys. Rev. B 89, 104512 (2014).

  4. Yu. G. Naidyuk, O.E. Kvitnitskaya, L. V. Tiutrina, I.K.Yanson, G. Behr, G. Fuchs, S.-L. Drechsler, K. Nenkov, and L. Schultz, Peculiarities of the superconducting gaps and the electron-boson interaction in TmNi2B2C as seen by point-contact spectroscopy, Phys. Rev. B, 2011,  Vol. 84, p.094516.

  5. Yu. G. Naidyuk, O.E. Kvitnitskaya, I.K.Yanson, G Fuchs, S Haindl, M Kidszun, L Schultz. and B.Holzapfel, Point-contact study of ReFeAsO1-xFx (Re = La, Sm) superconducting films, Superconductor Science and Technology.  2011,  Vol.24, p. 065010.

  6. N. L. Bobrov, V. N. Chernobay, Yu. G. Naidyuk, L. V. Tyutrina, D. G. Naugle, K. D. D. Rathnayaka, S. L. Bud’ko, P. C. Canfield, I. K. Yanson, Compe-tition of multiband superconducting and magnetic order in ErNi2B2C observed by Andreev reflection  Europhys. Lett. 2008, Vol. 83,  p. 37003.

  7. Yu. G. Naidyuk, O. E. KvitnitskayaI. K. Yanson, G. Fuchs, K. Nenkov, A. Waelte, G. Behr, D. Souptel, and S.-L. Drechsler, Point-contact spectroscopy of the antiferromagnetic superconductor HoNi2B2C in the normal and superconducting state, Phys. Rev. B, 2007,  Vol. 76, p.014520.

  8. D. L. Bashlakov, Yu. G. Naidyuk, I. K. Yanson, G. Behr, S.L. Drechsler, G. Fuchs, L. Schultz and D. Souptel, Point-contact spectroscopy of the nickel borocarbide superconductor YNi2B2C in the normal and superconducting state, J. Low  Temp. Physics, 2007,  Vol.147, p.335.

  9. I.K. Yanson, Yu.G. Naidyuk, Advances in point-contact spectroscopy: two-band superconductor MgB2 (review), Low Temp.Phys., 2004, Vol.30, p.261.

  10. Yu.G. Naidyuk, I.K. Yanson, Point-contact spectroscopy of the heavy-fermion systems (review). J. Phys. Condens. Matter, 1998, Vol.10, p.8905.

  11. I.K.Yanson, Contact spectroscopy of high-temperature superconductors (Review article). Part I: Physical and methodical fundamentals of contact spectroscopy of high-Tc superconductors. Experimental results for La2-xSrxCuO4 and their discussion. Sov.J.Low Temp.Phys., 1991, Vol.17, p.275.