Tunneling in pure and substituted single crystals of Bi2Sr2Ca1Cu2O8+χ: s+d-wave pairing and gap enhancement

Hancotte, Hugues; Deltour, Robert; Davydov, D. N.; Jansen, A. G. M.; Wyder, P.

doi:10.1016/s0921-4534(97)00850-2

Cited by 5 publications

(5 citation statements)

References 5 publications

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“…32 Very few publi-cations seem to have systematically studied the impurity effects in c-axis tunneling. We find one: Hancotte et al 33 showed that Zn substitution (≤ 1%) in the CuO 2 planes of BSCCO (2212) caused G(0) to markedly increase, accompanied by a reduced gap. Here the spectral weight of impurity effects is clearly large enough, yet not even a trace of a ZBCP was observed.…”

Section: Introductionmentioning

confidence: 74%

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Effect of unitary impurities on non-STM types of tunneling in high-Tcsuperconductors

Zhu

Ting

2000

Phys. Rev. B

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Based on an extended Hubbard model, we present calculations of both the local (i.e., singlesite) and spatially-averaged differential tunneling conductance in d-wave superconductors containing nonmagnetic impurities in the unitary limit. Our results show that a random distribution of unitary impurities of any concentration can at most give rise to a finite zero-bias conductance (with no peak there) in spatially-averaged non-STM type of tunneling. This is in spite of the fact that local tunneling in the immediate vicinity of an isolated impurity does show a conductance peak at zero bias. We also find that to give rise to even a small zero-bias conductance peak in the spatiallyaveraged type of tunneling the impurities must form dimers, trimers, etc. along the [110] directions. In addition, we find that the most-recently-observed novel pattern of the tunneling conductance around a single impurity by Pan et al. [Nature 403, 746 (2000)] can be explained in terms of a realistic model of the tunneling configuration which gives rise to the experimental results reported there. The key feature in this model is the blocking effect of the BiO and SrO layers which exist between the tunneling tip and the CuO2 layer being probed.

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Section: Introductionmentioning

confidence: 74%

“…Thus we propose that this is how impurities can possibly contribute to some of the observed ZBCP's, and why often ZBCP's are not observed in caxis non-localized tunneling, even in samples which have been deliberately introduced some substantial amount of substitutional non-magnetic zinc (Zn) impurities. 33…”

Section: B the Case Of Randomly Distributed Impuritiesmentioning

confidence: 99%

Effect of unitary impurities on non-STM types of tunneling in high-Tcsuperconductors

Zhu

Ting

2000

Phys. Rev. B

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“…Spontaneous time reversal symmetry breaking has also been predicted to occur around magnetic impurities doped into high-T c superconductors (Balatsky 1998). In fact, a large variation of the gap structure in Ni-doped BSCCO is reported by Hancotte et al (1997). The induced d x 2 +y 2 + is or d x 2 +y 2 + id xy states have no node in k-space, and a finite-amplitude gap opens for all directions.…”

Section: Btrs and Peak Splittingmentioning

confidence: 99%

Tunnelling effects on surface bound states in unconventional superconductors

Kashiwaya¹,

2000

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Recent studies on high-T c superconductors have aroused new interest in tunnelling effects in unconventional superconductors. Unlike in conventional s-wave superconductors, the d-wave pairing state in these materials has an internal phase of the pair potential. The internal phase as a function of the wavevector of the Cooper pairs has a large influence on the electric properties of tunnelling junctions. Important effects of the internal phase on the Josephson current were first predicted theoretically. The idea has been established through several experiments using high-T c Josephson junctions, which detect π -phase shift between the aand b-axis directions and fractional flux quanta. These results give convincing evidence for d-wave symmetry in high-T c superconductors. In addition, the existence of new interference effects in the quasiparticle states near surfaces and boundaries has been suggested through theoretical predictions. Experimentally, a large number of tunnelling spectroscopy data showed zero-bias conductance peaks (ZBCPs), the origin of which cannot be explained in terms of the classical concept that a tunnelling conductance spectrum is a phase-insensitive probe of the electronic states. It is clarified theoretically that the observed ZBCPs reflect the formation of zeroenergy states on the surface due to the π -phase shift of internal phase in the d-wave pairing symmetry. The formulation developed for tunnelling spectroscopy suggests that tunnelling spectroscopy is essentially phase sensitive. In addition, the formation of the bound states has been shown to have a serious influence on the electrical properties of Josephson junctions. Several anomalous properties including strong enhancement of the Josephson current in the low-temperature region have been predicted theoretically. In this report, recent developments in tunnelling effects on surface bound states in unconventional superconductors are reviewed.

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“…One should also note that in the superconducting state of Bi 2 Sr 2 CaCu 2 O 8+y , tunnel measurements of the nonsymmetrical junctions often show the dip in the bias V dependences of the differential conductivity G diff ns (V ) (about 10% magnitude as compared to the peak height) at about V ≈ −2 /e [463][464][465][466][467][468], whereas for symmetrical junctions the dips (or dip-hump structures) are observed at V ≈ ±3 /e [469][470][471]. The dependences G diff ns (V ) for the junctions involving Bi 2 Sr 2 CaCu 2 O 8+y are shown as typical examples of asymmetrical patterns in figures 8 and 9.…”

Section: High-t C Oxidesmentioning

confidence: 99%

Charge- and spin-density-wave superconductors

Gabovich

Войтенко

Annett

et al. 2001

Supercond. Sci. Technol.

170

147

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This review deals with the properties of superconductors with competing electron spectrum instabilities, namely, charge-density waves (CDWs) and spin-density waves (SDWs). The underlying reasons of the electron spectrum instability may be either Fermi surface nesting or the existence of Van Hove saddle points for lower dimensionalities. CDW superconductors include layered dichalcogenides, NbSe 3 , and compounds with the A15 and C15 structures among others. There is much evidence to show that high-T c oxides may also belong to this group of materials. The SDW superconductors include URu 2 Si 2 and related heavy-fermion compounds, Cr-Re alloys and organic superconductors. We review the experimental evidence for CDW and SDW instabilities in a wide range of different superconductors, and assess the competition between these instabilities of the Fermi surface and the superconducting gap. Issues concerning the superconducting order parameter symmetry are also touched upon. The accent is put on establishing a universal framework for further theoretical discussions and experimental investigations based on an extensive list of available and up-to-date references.

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Tunneling in pure and substituted single crystals of Bi2Sr2Ca1Cu2O8+χ: s+d-wave pairing and gap enhancement

Cited by 5 publications

References 5 publications

Effect of unitary impurities on non-STM types of tunneling in high-Tcsuperconductors

Effect of unitary impurities on non-STM types of tunneling in high-Tcsuperconductors

Tunnelling effects on surface bound states in unconventional superconductors

Charge- and spin-density-wave superconductors

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