Gap In Bi2Sr2CaCu2O8 Research Articles

Directly visualizing the sign change of d-wave superconducting gap in Bi2Sr2CaCu2O8+\u03b4 by phase-referenced quasiparticle interference

The superconducting state is formed by the condensation of Cooper pairs and protected by the superconducting gap. The pairing interaction between the two electrons of a Cooper pair determines the gap function. Thus, it is pivotal to detect the gap structure for understanding the mechanism of superconductivity. In cuprate superconductors, it has been well established that the gap may have a d-wave function. This gap function has an alternative sign change in the momentum space. It is however hard to visualize this sign change. Here we report the measurements of scanning tunneling spectroscopy in Bi2Sr2CaCu2O8+δ and conduct the analysis of phase-referenced quasiparticle interference (QPI). We see the seven basic scattering vectors that connect the octet ends of the banana-shaped contour of Fermi surface. The phase-referenced QPI clearly visualizes the sign change of the d-wave gap. Our results illustrate an effective way for determining the sign change of unconventional superconductors.

Impurity Effects on Energy Gap in Bi2Sr2CaCu2O8+y Investigated by Electronic Raman Scattering

The Raman scattering experiments were carried out in Zn-doped and Zn-free Bi 2 Sr 2 CaCu 2 O 8+y with optimal hole concentration below and above T c . The energy of pair-breaking peak in the B 1g Raman spectrum, corresponding to the magnitude of superconducting gap 2Δ 0 , is suppressed by 1% Zn-doping. In the normal state, the B 1g Raman spectrum for Zn-doped sample shows no pseudogap behaviour, suggesting that the pseudogap is strongly smeared by Zn-doping.

Anisotropy of the electronic structure and superconducting gap in Bi2Sr2CaCu2O8.

Anisotropy of the electronic structure and superconducting gap in Bi2Sr2CaCu2O8.

Dx 2-y 2-like superconducting gap in Bi2Sr2CaCu2O6 observed by angle-resolved photoemission

A large anisotropy of superconducting energy gap in Bi2Sr2CaCu2O8 was directly observed by high-energy resolution angle-resolved photoemission spectroscopy with a high-quality twin-free single crystal. The superconducting gap (Δ) observed in the ΓM direction is 17–19 meV while that in the ΓX (or ΓY) direction is 0–2 meV, suggesting the dx 2−y 2 superconducting order parameter.

Superconducting energy gap in Bi2Sr2CaCu2O8 observed by high-resolution photoemission spectroscopy

A high-energy resolved low-temperature photoemission spectrometer of angle-integrated mode was constructed to study the detailed electronic structure near the Fermi level of novel materials, in particular, cuprate high-Tc superconductors. Photoemission measurement with this spectrometer on a Bi2Sr2CaCu2O8 polycrystal clearly showed a transfer of spectral weight from the vicinity of the Fermi level to the higher binding-energy region below the superconducting transition temperature, indicating opening of the superconducting gap. Numerical simulation for both normal and superconducting states showed that the superconducting gap parameter (Δ) of 18 meV with dx 2−y 2 symmetry gives a most reasonable fitting.

Detection of an anisotropy of the superconducting gap in Bi2Sr2CaCu2O8+δ single crystals by Raman and tunneling spectroscopy

Abstract We report on polarized Raman spectra and tunneling measurements on the (010)-and (001)-planes of Bi2Sr2CaCu2O8+δ single crystals in the temperature range from 5 K up to room temperature. The Raman continuum of electronic excitations in the normal state of the Bi-2212 compound is redistributed below Tc. In the Ag symmetry, a superconducting gap is detected, which scales with Tc for different crystals and which is strongly anisotropic for different scattering configurations. While in the Y(Z, Z)Ȳ scattering geometry the gap energy amounts to 2ΔZZ(0)/kBTc=3.5±0.1, a value of 2ΔXX(0)/kBTc=5.7±0.2 is found for the gap energy in the Y(X, X) Ȳ scattering geometry. Tunneling measurements confirm the existence of the gap anisotropy in the Bi-2212 superconductor and yield gap values of 2Δ(0)ZZ/kBTc=3.5±0.2 and 2Δ(0)xx/kBTc=5.8±0.3. The temperature dependence of the gaps has been measured by means of Raman spectroscopy. In Y(Z, Z) Ȳ scattering geometry at T/Tc=0.96, the gap is reduced by less than 10% of its value at 5 K. This reduction amounts to 30% for the gap in Y(X, X) Ȳ scattering geometry. Consequently, the temperature dependence of both gaps differs strongly from the BCS behavior.

Superconducting gap in Bi2Sr2CaCu2O8.

Reflectivity measurements, at different fixed frequencies, have been performed on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} films as a function of temperature and magnetic field. Analysis of the data provides evidence for an order parameter 2{Delta}(0){congruent}3.3{ital k}{sub {ital B}T{ital c}} although the variation of this order parameter with temperature is significantly different from that predicted by the weak-coupling BCS model.