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Journal of Low Temperature Physics

, Volume 179, Issue 1–2, pp 108–112 | Cite as

Observation of a Bulk Nodal-Gap in Overdoped Y\(_{0.9}\)Ca\(_{0.1}\)Ba\(_{2}\)Cu\(_{3}\)O\(_{7-\delta }\) Thin Films

  • N. BacharEmail author
  • Y. Bechor
  • B. Gorshunov
  • E. Farber
Article

Abstract

Complex conductivity of overdoped Y\(_{0.9}\)Ca\(_{0.1}\)Ba\(_{2}\)Cu\(_{3}\)O\(_{7-\delta }\) thin films was measured in Terahertz frequency using frequency and time domain methods. The films were measured in the frequency range of 3–100 cm\(^{-1}\) and in the temperature range of 20–300 K. Results show a possible deviation from a pure \(d_{x^{2}-y^{2}}\)-wave superconductor, indicated by the existence of an energy sub-gap in overdoped Y\(_{0.9}\)Ca\(_{0.1}\)Ba\(_{2}\)Cu\(_{3}\)O\(_{7-\delta }\) films. Evidence for this sub-gap appears as non-monotonic behavior of \(\sigma _{1}(\omega ,T)\) as a function of frequency followed by a sharp decrease at low frequencies, and a dip in the imaginary part of the optical conductivity multiplied by frequency, \(\omega {{\sigma }_{2}}(\omega ,T)\). The mentioned features were observed at energy of about 1.2 meV in 10 % Ca-doped YBCO thin films. Our complex conductivity spectra are in agreement with the theoretical prediction obtained by using a mixed symmetry order parameter within the Born limit, shown by Schürrer et al. We suggest that these observations are direct evidence for a nodal gap obtained in a \(d_{x^{2}-y^{2}}\)-wave superconductor and can be theoretically clarified by adding an imaginary component as \(is\) or \(i{{d}_{xy}}\) to the main \(d_{x^{2}-y^{2}}\)-wave order parameter.

Keywords

YBCO Pairing Symmetry THz spectroscopy 

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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  1. 1.Laboratory for Superconductivity and Optical SpectroscopyAriel UniversityArielIsrael
  2. 2.Prokhorov Institute of General PhysicsRussian Academy of SciencesMoscowRussia

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