Recent observation of anomalous superconducting behavior of ultrathin YBCO films and single crystals of cluster borides

• Published in: Физика низких температур
• Date: 2006
• Main Author: Gasparov, V.A.
• Format: Article
• Language: English
• Published: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2006
• Subjects: К 100-летию со дня рождения Б.Г. Лазарева
• Online Access: https://nasplib.isofts.kiev.ua/handle/123456789/120350
• Journal Title: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Cite this: Recent observation of anomalous superconducting
 behavior of ultrathin YBCO films and single crystals
 of cluster borides / V.A. Gasparov // Физика низких температур. — 2006. — Т. 32, № 8-9. — С. 1105–1114. — Бібліогр.: 33 назв. — англ.

We report the number of deviations from conventional behavior in superconducting properties
 of ultrathin (1–3 unit-cell (UC)) YBa₀₂Cu₃O₇₋x films sandwiched between semiconducting
 Pr₀,₆Y₀,₄Ba₂Cu₃O₇₋x layers and for single crystals of cluster superconductor: dodecaboride ZrB₁₂.
 We have found a quadratic temperature dependence of the kinetic inductance, Lk⁻¹(Т)
 , at low temperatures
 independent of frequency, with a break in slope at TBKT
 dc , the maximum of real part of
 conductance, ωσ₁(T), and a large shift of the break temperature and the maximum position to
 higher temperatures with increasing frequency ω. We obtain from these data the universal ratio
 T /Lk⁻¹
 (Tdc ) = 25, 25, and 17 nHK for 1-, 2- and 3-UC films, respectively in close agreement
 with theoretical prediction for vortex—antivortex unbinding transition. Superfluid density of
 ZrB₁₂ displays unconventional temperature dependence with pronounced shoulder at T/Tc equal
 to 0.65. Contrary to conventional theories we found a linear temperature dependence of Hс₂(Т)
 from Tc down to 0.35 K. We suggest that both λ(T) and Hс₂(Т) dependencies can be explained by a
 two band BCS model with different superconducting gap and Tc.