Tunnelling evidence for predominantly electron–phonon coupling in superconducting Ba1−xKxBiO3 and Nd2−xCexCuO4−y

Huang, Qiang; Zasadzinski, J. F.; Tralshawala, N.; Gray, K. E.; Hinks, D. G.; Peng, J. L.; Greene, R. L.

doi:10.1038/347369a0

Cited by 285 publications

(113 citation statements)

References 12 publications

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“…The analysis of this material is of particular interest with respect to the question whether or not there is a change in sign of the order parameter for NCCO. Up to now, there is convincing experimental evidence that NCCO has a dominating s-wave symmetry of the order parameter [18,19,20,21], i.e., the order parameter of NCCO is expected to show no change in sign for different k-directions. Hence, Andreev bound states are expected only for hole doped HTS, which are believed to have a dominating dwave symmetry of the order parameter, but should be absent for NCCO.…”

Section: Introductionmentioning

confidence: 99%

Andreev bound states in high temperature superconductors

et al. 1998

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Abstract. Andreev bound states at the surface of superconductors are expected for any pair potential showing a sign change in different k-directions with their spectral weight depending on the relative orientation of the surface and the pair potential. We report on the observation of Andreev bound states in high temperature superconductors (HTS) employing tunneling spectroscopy on bicrystal grain boundary Josephson junctions (GBJs). The tunneling spectra were studied as a function of temperature and applied magnetic field. The tunneling spectra of GBJ formed by YBa2Cu3O 7−δ (YBCO), Bi2Sr2CaCu2O 8+δ (BSCCO), and La1.85Sr0.15CuO4 (LSCO) show a pronounced zero bias conductance peak that can be interpreted in terms of Andreev bound states at zero energy that are expected at the surface of HTS having a d-wave symmetry of the order parameter. In contrast, for the most likely s-wave HTS Nd1.85Ce0.15CuO4−y (NCCO) no zero bias conductance peak was observed. Applying a magnetic field results in a shift of spectral weight from zero to finite energy. This shift is found to depend nonlinearly on the applied magnetic field. Further consequences of the Andreev bound states are discussed and experimental evidence for anomalous Meissner currents is presented.

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Section: Introductionmentioning

confidence: 99%

Andreev bound states in high temperature superconductors

et al. 1998

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“…However, as can already be seen from the differences of the generic phase diagram on the electron-and hole-doped side, the physics of electron-and hole-doped HTS is different. In particular, the order parameter (OP) symmetry of the electron-doped cuprates is most likely of s-wave type [2][3][4][5], in contrast to the d-wave OP symmetry in the hole-doped HTS. To clarify the specific differences and similarities between the electron-and hole-doped HTS a more detailed experimental study of the electron-doped HTS is required.…”

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Anomalous Low Temperature Behavior of SuperconductingNd1.85Ce0.15CuO4−

Alff¹,

Meyer²,

Kleefisch³

et al. 1999

Phys. Rev. Lett.

119

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We have measured the temperature dependence of the in-plane London penetration depth λ ab (T ) and the maximum Josephson current Ic(T ) using bicrystal grain boundary Josephson junctions of the electron-doped cuprate superconductor Nd1.85Ce0.15CuO4−y. Both quantities reveal an anomalous temperature dependence below about 4 K. In contrast to the usual monotonous decrease (increase) of λ ab (T ) (Ic(T )) with decreasing temperature, λ ab (T ) and Ic(T ) are found to increase and decrease, respectively, with decreasing temperature below 4 K resulting in a non-monotonous overall temperature dependence. This anomalous behavior was found to be absent in analogous measurements performed on Pr1.85Ce0.15CuO4−y. From this we conclude that the anomalous behavior of Nd1.85Ce0.15CuO4−y is caused by the presence of the Nd 3+ paramagnetic moments. Correcting the measured λ ab (T ) dependence of Nd1.85Ce0.15CuO4−y for the temperature dependent susceptibility due to the Nd moments, an exponential dependence is obtained indicating isotropic s-wave pairing. This result is fully consistent with the λ ab (T ) dependence measured for Pr1.85Ce0.15CuO4−y. The vast majority of experiments on the cuprate superconductors are performed on hole-doped materials. Much less attention has been paid to the system Ln 2−x Ce x CuO 4−y (with Ln = Pr, Nd, Sm, Eu) [1] which represents an electron-doped material. Both hole-and electron-doped cuprates have in common the copper oxygen planes as the central building blocks of the high-temperature superconductors (HTS) suggesting similar superconducting properties. However, as can already be seen from the differences of the generic phase diagram on the electron-and hole-doped side, the physics of electron-and hole-doped HTS is different. In particular, the order parameter (OP) symmetry of the electron-doped cuprates is most likely of s-wave type [2][3][4][5], in contrast to the d-wave OP symmetry in the hole-doped HTS. To clarify the specific differences and similarities between the electron-and hole-doped HTS a more detailed experimental study of the electron-doped HTS is required.

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“…To clarify this issue we have studied [001] tilt NCCO-GBJs. Since for the electron doped material NCCO there is convincing experimental evidence for a s-wave symmetry of the OP [10][11][12][13], NCCO-GBJs represent an interesting model system to test the influence of the OP symmetry on the transport properties of GBJs.…”

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confidence: 99%

Superconducting Nd1.85Ce0.15CuO4−y bicrystal grain boundary Josephson junctions

Kleefisch

Alff

Schoop

et al. 1998

Applied Physics Letters

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We have studied the electric transport properties of symmetrical [001] tilt Nd1.85Ce0.15CuO4−y (NCCO) bicrystal grain boundary Josephson junctions (GBJs) fabricated on SrTiO3 bicrystal substrates with misorientation angles of 24 • and 36.8 • . The superconducting properties of the NCCOGBJs are similar to those of GBJs fabricated from the hole doped high temperature superconductors (HTS). The critical current density Jc decreases strongly with increasing misorientation angle. The products of the critical current Ic and the normal resistance Rn (∼ 100 µV at 4.2 K) are small compared to the gap voltage and fit well to the universal scaling law IcRn ∝ √ Jc found for GBJs fabricated from the hole doped HTS. This suggests that the symmetry of the order parameter, which most likely is different for the electron and the hole doped HTS has little influence on the characteristic properties of symmetrical [001] tilt GBJs. PACS: 74.25.Fy, 74.50.+r Applied Physics Letters to be published June 1, 1998Bicrystal grain boundary Josephson junctions (GBJs) have been studied intensively using epitaxial thin films of the various hole doped high temperature superconductors (HTS) [1][2][3]. However, there is very limited information on GBJs fabricated from the electron doped material Nd 1.85 Ce 0.15 CuO 4−y (NCCO) [4]. For the vast majority of GBJs the transport properties can be well described within the intrinsically shunted junction (ISJ) model [2,5,6]. In this model a continuous, but spatially inhomogeneous insulating grain boundary barrier is assumed that contains a high density of localized defect states. The localized states allow for resonant tunneling of quasiparticles providing an intrinsic resistive shunt, whereas resonant tunneling of Cooper pairs is prevented by Coulomb repulsion. This results in reduced I c R n products and a scaling behavior I c R n ∝ √ J c observed in many experiments [2,[5][6][7]. Meanwhile, it is well established that most hole doped HTS have a dominant d-wave component of the order parameter (OP) [8]. The influence of the d-wave symmetry of the OP on the magnetic field dependence of I c has been shown for asymmetric 45 • tilt YBCO-GBJs [9]. So far, in the ISJ-model the likely d-wave pairing state of the hole doped HTS has not been taken into account and the relevance of the d-wave symmetry of the OP for the characteristic properties of symmetrical [001] tilt GBJs such as the small value and the scaling behavior of the I c R n product is still a point of controversy. To clarify this issue we have studied [001] tilt NCCO-GBJs. Since for the electron doped material NCCO there is convincing experimental evidence for a s-wave symmetry of the OP [10-13], NCCO-GBJs represent an interesting model system to test the influence of the OP symmetry on the transport properties of GBJs.The NCCO-GBJs were fabricated by molecular beam epitaxy (MBE) of c-axis oriented NCCO thin films on SrTiO 3 bicrystal substrates. The substrate temperature during growth was about 730 • C and ozone was used as oxidation gas. For ...

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Tunnelling evidence for predominantly electron–phonon coupling in superconducting Ba1−xKxBiO3 and Nd2−xCexCuO4−y

Cited by 285 publications

References 12 publications

Andreev bound states in high temperature superconductors

Andreev bound states in high temperature superconductors

Anomalous Low Temperature Behavior of SuperconductingNd1.85Ce0.15CuO4−

Superconducting Nd1.85Ce0.15CuO4−y bicrystal grain boundary Josephson junctions

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