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BCS d-wave behavior in the terahertz electrodynamic response of electron-doped cuprate superconductors

Zhenisbek Tagay, Fahad Mahmood, Anaelle Legros, Tarapada Sarkar, Richard L. Greene, and N. P. Armitage
Phys. Rev. B 104, 064501 – Published 2 August 2021
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  • INTRODUCTION
  • METHODS
  • EXPERIMENTAL RESULTS
  • PREVENTING THE CONTRIBUTION OF C-AXIS…
  • CONCLUSION
  • ACKNOWLEDGMENTS
    • References

    Abstract

    Although cuprate superconductors have been intensively studied for the past decades, there is no consensus regarding the microscopic origin of their superconductivity. In this paper, we measure the low-energy electrodynamic response of slightly underdoped and overdoped La2−xCexCuO4 thin films using time-domain terahertz (THz) spectroscopy to determine the temperature and field dependence of the superfluid spectral weight. We show that the temperature dependence obeys the relation ns ∝1−(T/Tc)2, typical for dirty limit BCS-like d-wave superconductors. Furthermore, the magnetic field dependence was found to follow a sublinear B form, which supports predictions based on a d-wave symmetry for the superconducting gap. These observations imply that the superconducting order in these electron-doped cuprates can be well described in terms of a disordered BCS d-wave formalism.

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    • Received 6 December 2020
    • Revised 22 June 2021
    • Accepted 19 July 2021

    DOI:https://doi.org/10.1103/PhysRevB.104.064501

    ©2021 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Optical conductivitySuperconducting gapSuperfluid density
    1. Physical Systems
    High-temperature superconductorsThin films
    1. Techniques
    BCS theoryTerahertz spectroscopy
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Zhenisbek Tagay1, Fahad Mahmood1,2,3, Anaelle Legros1, Tarapada Sarkar4, Richard L. Greene4, and N. P. Armitage1

    • 1Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA
    • 2Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
    • 3F. Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
    • 4Department of Physics, Maryland Quantum Materials Center, University of Maryland, College Park, Maryland 20742, USA

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    Issue

    Vol. 104, Iss. 6 — 1 August 2021

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    Images

    • Figure 1
      Figure 1

      (a) Real and (b) imaginary parts of optical conductivity for overdoped LCCO (x = 0.13) as a function of frequency and temperature. (c) ωσ2 derived from σ2(ω) data. Dashed lines indicate quadratic extrapolation to ω=0.

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    • Figure 2
      Figure 2

      Drude fits to σ(ω) near Tc (a) x=0.13, Tc=21 K and (b) x=0.1, Tc=19 K.

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    • Figure 3
      Figure 3

      (a) Temperature dependence of the superfluid spectral weight Ssc for the x=0.13 sample. Red dashed line denotes quadratic fit. (b) Fitting σ1(ω) to Drude (low frequency) and linear forms (high frequency). Grey dashed lines are extrapolations as described in the text. (c) Comparison of Ssc obtained using 2 different methods.

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    • Figure 4
      Figure 4

      (a) Real and (b) imaginary parts of optical conductivity for overdoped LCCO (x = 0.13) at different magnetic fields. (c) Superfluid spectral weight Ssc at different temperatures as a function of applied magnetic field. Dashed lines indicate linear fit.

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    • Figure 5
      Figure 5

      Complex conductivity of x = 0.1 underdoped sample at: [(a),(b)] different temperatures (B = 0 T); [(d),(e)] different magnetic fields (T = 4.8 K). (c) Temperature and (f) field dependence of extracted superconducting spectral weight Ssc. Red dashed line denotes quadratic fit to data. Black dashed line indicates linear fit.

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    • Figure 6
      Figure 6

      [(a),(b)] Real and imaginary part, respectively, of the measured in-plane conductivity of LCCO x = 0.13 as a function of frequency, at T = 5 K, for various polarizations of the incident THz beam (changing the angle Φ of the linear polarization). [(c),(d)] Real and imaginary part, respectively, of the calculated in-plane σeff as a function of frequency, in the case of a contribution of the c-axis conductivity via a tilt angle α. The conductivity is calculated for different angles α, using for σab the actual data from (a) and (b) at Φ=−45∘, and for σc the extracted data at x = 0.081 and T = 2.5 K of reference Pimenov et al. [31].

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