Unusual microwave response and bulk conductivity of very thin FeSe₀.₃Te₀.₇ films as a function of temperature

• Published in: Физика низких температур
• Date: 2014
• Main Authors: Barannik, A.A., Cherpak, N.T., Yun Wu, Sheng Luo, Yusheng He, Kharchenko, M.S., Porch, A.
• Format: Article
• Language: English
• Published: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2014
• Subjects: Свеpхпpоводимость, в том числе высокотемпеpатуpная
• Online Access: https://nasplib.isofts.kiev.ua/handle/123456789/119522
• Journal Title: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Cite this: Unusual microwave response and bulk conductivity of very thin FeSe₀.₃Te₀.₇ films as a function of temperature / A.A. Barannik, N.T. Cherpak, Yun Wu, Sheng Luo, Yusheng He, M.S. Kharchenko, A. Porch // Физика низких температур. — 2014. — Т. 40, № 6. — С. 636-644. — Бібліогр.: 31 назв. — англ.

Results of X-band microwave surface impedance measurements of FeSe₁–xTex very thin film are reported. The effective surface resistance shows appearance of peak at T ≤ Tc when plotted as a function of temperature. The authors suggests that the most well-reasoned explanation can be based on the idea of the changing orientation of the microwave magnetic field at a S–N phase transition near the surface of a very thin film. The magnetic penetration depth exhibits a power-law behavior of L(T) CTn, with an exponent n ≈ 2.4 at low temperatures, which is noticeably higher than in the published results on FeSe₁–xTex single crystal. However the temperature dependence of the superfluid conductivity remains very different from the behavior described by the BCS theory. Experimental results are fitted very well by a two-gap model with Δ₁/kTc = 0.43 and Δ₂/kTc = 1.22, thus supporting s±-wave symmetry. The rapid increase of the quasiparticle scattering time is obtained from the microwave impedance measurements.