Tunneling spectroscopy of superconductingNd1.85Ce0.15

Abstract

The superconducting electronic states of Nd 1.85 Ce 0.15 CuO 4Ϫ␦ ͑NCCO͒ are studied by applying the phasesensitive capability of tunneling spectroscopy. Unlike the YBa 2 Cu 3 O 7Ϫ␦ cases, the conductance spectra measured on ͑100͒-, ͑110͒and ͑001͒-oriented surfaces showed V-shaped gap structures, and no zero-bias conductance peaks were observed even around steps on the surfaces. The present results reject the possibility of d x 2 Ϫy 2-wave and d xy -wave symmetries for the pair potential in NCCO. The experimental spectra are well fitted to theoretical curves of anisotropic s-wave symmetry with a large smearing factor.

Distinct pairing symmetries inNd1.85Ce0.15CuO4−yandLa1.89

“…12. The lowest value of A = 17% achieved in this work is much smaller than the previous report of A ≈ 1 by STM measurements on NCCO single crystal [13].…”

“…To sum up the main characteristics of the measured spectra, we note that all the spectra are near the tunneling limit with two clear coherence peaks at symmetric positions of the bias voltage (much sharper than that of the previous works studied by both STM [13,29] and point contact [30]) with no Andreev reflection-like spectrum. Second, the spectral shape is nearly identical for the (110) and (100) directions.…”

“…In addition, Raman scattering [10] and recent ARPES [11] experiments show a nonmonotonic d-wave order parameter. However, this has been contrasted by tunnelling [12,13] and some other specific heat [14] and penetration depth measurements [15,16,17]. In particular, there may be a crossover from d-wave to s-wave symmetries by changing the doped electron concentration [18,19] or decreasing temperature [20].…”

“…In Ref. [13], the authors ascribed the unphysically large A (A = Γ/∆ ∼ 1) to the unreasonable assumption of isotropic s-wave symmetry. They found that if the maximum value of Γ/∆ was assumed to be 0.2 similar to YBCO, reasonable fitting is obtained by assuming anisotropic s-wave symmetry, namely, ∆(θ) = ∆ 0 + ∆ 1 cos(4θ).…”

Pseudogap Phenomena and Superconducting Fluctuations in Hubbard Model for High-TcCuprates

“…The exponential dependence of the magnetic penetration depth has been reported. 93) The absence of the zero bias conductance peak is also reported 94) while it should exist in the d-wave superconductor. 95) The possibility of some node-less superconductivity has been proposed theoretically.…”