Eliashberg Analysis of Tunneling Experiments: Support for the Pairing Glue Hypothesis in Cuprate Superconductors

Abstract

Evidence for the validity of the pairing glue interpretation of high temperature superconductivity is presented using a modified Eliashberg analysis of experimental superconductor-insulator-superconductor (SIS) tunneling data in B 2 Sr 2 CaCu 2 O 8 (Bi2212) over a wide range of doping. This is accomplished by extracting detailed information on the diagonal and anomalous contributions to the quasiparticle selfenergy. In particular, a comparison of the imaginary part of the anomalous self-energy ImÈð!Þ and the pairing glue spectral function 2 Fð!Þ used in the model is consistent with Hubbard model simulations in the literature. In addition, the real part of the diagonal self-energy for optimal doped Bi2212 bears a strong resemblance to that obtained from photoemission experiments.

Eliashberg analysis of Bi2Sr2CaCu2O8+δ intrinsic tunneling spectra

“…The quantities of /ðxÞ, as well as the frequency-dependent pairing interaction calculated from the Hubbard and t-J models are found to have a close resemblance to the results for Pb, with SF replacing the phonons [3,4]. These results provide a solid theoretical basis for the SF-mediated pairing in the cuprates [1,2] and are tested recently in the tunneling experiment of Bi 2 Sr 2 CaCu 2 O 8þd (Bi2212) [8]. Eliashberg analysis of the tunneling data at the temperature of 4.2 K for various doping shows that the imaginary part of the pairing function Im/ðxÞ, the real part of the diagonal self-energy ReRðxÞ ¼ x½1 À ReZðxÞ, and the pairing glue spectral function a 2 FðXÞ are consistent with the Hubbard model simulations [3,4], which lend a strong support for the SF-mediated pairing in the materials.…”

“…With this, the Eliashberg equations can be written, either on the real frequency axis [8][9][10] or on the imaginary frequency axis [20,21], in the form that closely resembles the classical s-wave situation [5][6][7]. In the real frequency axis formalism we have [8][9][10]:…”

“…In this case, the pairing interaction is retarded, similar to the situation in BCS conventional superconductors where electron pairing is mediated by phonons [5][6][7]. Spectroscopic studies and analysis based upon the strong-coupling Eliashberg theory have been performed for the cuprate superconductors in a variety of experiments such as electron tunneling [8][9][10], infrared conductivity [11,12], and angle-resolved photoemission spectroscopy (ARPES) [13,14].…”

From Cooper-pair glass to unconventional superconductivity: a unified approach to cuprates and pnictides

“…Just beyond the insulating phase, the SC dome appears in the phase diagram as a function of carrier concentration between two critical points. Understanding the transition from such an insulating to SC state is still a major challenge.Microscopic measurements reveal an unconventional quasiparticle (QP) dispersion, the 'peak-dip-hump' structure [2], often attributed to the coupling to a collective mode [3][4][5][6][7][8]. Although the peak to dip energy follows both the neutron resonance and T c as a function of doping [6,9,10], the finer shape of the QP spectra and their temperature dependence remain a challenge.…”

Disentangling the Electronic and Phononic Glue in a High- T c Superconductor

“…Inelastic neutron and X-ray scattering experiments found evidence for both QP-phonon anomalies [8] and bosonic excitations attributed to spin fluctuations [7,9] and loop currents [10]. Dip features in tunnelling experiments have been used to alternatively support the scenarios of dominant electron-phonon interactions [11] or antiferromagnetic spin fluctuations [12]. The frequency-dependent dissipation of the Drude optical conductivity, σ (ω), measured by equilibrium optical spectroscopies, has been interpreted [13][14][15] as the coupling of electrons to bosonic excitations, in which the separation of the phononic and electronic contributions is impeded by their partial coexistence on the same energy scale (<90 meV).…”