Analysis of the pseudogap-related structure in the tunnel spectra of superconducting Bi2Sr2CaCu2O8+δ revealed by break-junction technique

Abstract

Tunnel conductance G V( ) for break-junctions made of as-grown single-crystal Bi 2 Sr 2 CaCu 2 O 8+d samples with T c » -86 89 K was measured and clear-cut dip-hump structures (DHSs) were found in the range 80 120 -mV of the bias voltage V . The theory of tunneling in symmetric junctions between inhomogeneous charge-density-wave (CDW) superconductors, considered in the framework of the s-pairing model, has been developed. CDWs have been shown to be responsible for the appearance of the DHS in the tunnel current-voltage characteristics and properly describes experimental results.

Gap Structures of A-15 Alloys from the Superconducting and Normal-State Break-Junction Tunnelling

“…Furthermore, although the strong-coupling feature of the electron-phonon interac- tion should be concomitant with the ideal BCS-like gap structures, no such hump is observed along with the very distinct BCS gap structure of Figure 3 (a). On the other hand, it seems remarkable that the coexisting superconducting-gap and hump structures presented here are very similar to the tunnelling conductance patterns of the high-T c copper-oxide superconductors observed at low T [16,33], although the energy scales differ in both cases [27]. We note that a misleading interpretation of the outer structures as a strong-coupling effect was discussed earlier in the case of a 5f-electron superconductor [40].…”

“…The contest between superconducting and CDW (dielectric) order parameters should inevitably lead to a superposition of the corresponding energy gaps in the overall electron spectrum modified by both Cooper and electron-hole pairings. Any experimental technique measuring the gapped electron density of states below T c or the convolution with its counterpart (if any) should be sensitive to the interplay between phenomena discussed above [15][16][17]. A typical example of such a method is electronic quasi-particle tunnelling spectroscopy.…”

“…According to earlier findings in the point-contact measurements [31], we expected the manifestations of CDWs also in the quasi-particle conductance G(V) = dI/dV, where I denotes the quasi-particle tunnel current across the break junction. The quantity G(V) in CDW superconductors is a complicated functional of the superconducting, Δ, and dielectric (CDW), Σ, energy gaps [15,16,33] being no more a simple convolution of the electron density of states as in the conventional Bardeen-Cooper-Schrieffer (BCS) model of superconductivity [36]. From the experimental point of view, tunnel conductances G(V) distorted by CDW gapping are well known for a number of relevant materials [15,16,37,38].…”

Tunneling spectra of break junctions involving Nb3Sn

“…At the same time, a coexistence in the conductance spectra of the superconducting and smeared hump structures resembles the features found in tunneling conductance of the high-T cupper-oxide superconductors at low temperatures [12]. The similarity between the hump feature at ± 20 mV and the normal-state gap manifestation in the high-T superconductor can be inferred from Fig.…”

Spatial distribution of superconducting and charge-density-wave order parameters in cuprates and its influence on the quasiparticle tunnel current (Review Article)

“…Both CDWs and the electronic nonhomogeneity should be crucial for tunnel spectroscopy, which studies voltage, V , dependences of the quasiparticle current J and the corresponding conductance ( ) = / G V dJ dV [52][53][54][55][56]. Some time ago we suggested that CDWs have already been detected in the quasiparticle tunnel current-voltage characteristics [30,[57][58][59][60]. Specifically, ( ) G V of junctions (either symmetric or nonsymmetric ones) involving high-c T oxides reveal peak-diphump structures at energies eV much larger than the superconducting gap-edge positions ∆ [25,31,55,61,62].…”