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

Abstract

We used point-contact tunnelling spectroscopy to study the superconducting pairing symmetry of electron-doped N d1.85Ce0.15CuO4−y (NCCO) and hole-doped La1.89Sr0.11CuO4 (LSCO). Nearly identical spectra without zero bias conductance peak (ZBCP) were obtained on the (110) and (100) oriented surfaces (the so-called nodal and anti-nodal directions) of NCCO. In contrast, LSCO showed a remarkable ZBCP in the nodal direction as expected from a d-wave superconductor. Detailed analysis reveals an s-wave component in the pairing symmetry of the NCCO sample with ∆/kBTc = 1.66, a value remarkable close to that of a weakly coupled BCS superconductor. We argue that this s-wave component is formed at the Fermi surface pockets centered at (±π,0) and (0,±π) although a d-wave component may also exist.

Nearly isotropics-wave gap in the bulk of the optimally electron-doped superconductorNd1.85Ce0.15Zhao1 2010Phys. Rev. B172120View full textAdd to dashboardCite

“…Based on the BTK theory, Shan et al calculate the tunneling conductance in terms of the isotropic s-wave gap function. 17 The agreement between the calculated curve and data is excellent for each tunneling spectrum. However, the gap sizes that used to fit the tunneling spectra along the ͑100͒ and ͑110͒ directions are slightly different.…”

“…12 But the same data can be quantitatively explained 7 in terms of a nodeless s-wave gap if one takes into account an extrinsic effect due to current-induced nucleation of vortex-antivortex pairs at defects. Extensive penetration depth data 13 of Pr 2−x Ce x CuO 4−y confirmed the nodeless gap symmetry at all the doping levels except for a deeply underdoped Pr 1.885 Ce 0.115 CuO 4−y sample with T c =12 K. Point-contact tunneling spectra [14][15][16][17][18] also showed no zero-bias conductance peak ͑ZBCP͒ at all the doping levels except for a deeply underdoped Pr 1.87 Ce 0.13 CuO 4−y with T c =12 K. Therefore, the penetration depth and point-contact tunneling spectra consistently suggest that the gap symmetry in deeply underdoped samples should be d wave and change to a nodeless s wave when the doping level is above a critical value, in agreement with the theoretical prediction based on a phononmediated pairing mechanism. 19 This scenario can also ex-plain the d-wave gap symmetry inferred from surfacesensitive experiments if surfaces or interfaces are deeply underdoped.…”

Understanding electron-doped cuprate superconductors as hole superconductors

“…Furthermore, this remains true for both Nd 1.85 Ce 0.15 CuO 4−y at optimal doping (subject of Ref. [79]) and for Pr 1−x Ce x CuO 4−y as a function of doping, as shown in Ref. [80] (see their Fig.…”

The Superconducting Order Parameter in High-Tc Superconductors – A Point-Contact Spectroscopy Viewpoint

“…Since our junctions are all in the low-Z regime, an anomalous proximity effect (already discussed above for YBCO) cannot be excluded as the origin of the subdominant imaginary OP component [43]. This could be the case since more recent PCS measurements in underdoped LSCO in the tunneling (high Z ) regime [51] have given spectra with symmetric conductance maxima in the (100) direction and a clear ZBCP in the (110) direction, as expected for a pure d -wave symmetry. It is worth noting that, in any case, these findings confirm that the gap measured by PCARS is different from that measured by tunnel or ARPES measurements, which decreases monotonically with doping (see fig.3f and g).…”