Tracing the electronic pairing glue in unconventional superconductors via inelastic Scanning Tunneling Spectroscopy

Abstract

The origin of Cooper pairing in high-temperature superconductors, such as the copper-oxide and iron-based system, is still under debate. High transition temperatures together with unconventional pairing states support the picture of an electronic pairing glue in the cuprates, where superconductivity is mediated by collective bosonic excitations of the electron fluid. In other materials, most importantly iron based systems with only hole or only electron pockets, the microscopic origin is hotly debated. Scanning tunneling microscopy (STM) has been shown to be a powerful experimental probe to detect electronic excitations and further allows to deduce some fingerprints of bosonic collective modes. Here, we demonstrate that the inclusion of inelastic tunnel events is crucial for the interpretation of tunneling spectra and allows to directly probe bosonic excitations via STM. We develop a model describing both the elastic tunneling current, which displays the electronic spectral function, and the inelastic current, that contains the information about the bosonic spectrum, in the superconducting state. Adopting this extended tunneling formalism we can naturally reproduce the tunneling spectra of various unconventional superconductors and trace the occurring features back to an opening of a spin gap in the superconducting state. More generally, our approach is a strong argument in favour of a collective mode mediating the pairing state in particular in iron-based systems. In particular, we conclude that the debated pairing mechanism in LiFeSe is also of electronic origin with sign-changing pairing symmetry.

7 pages, 4 figures, +Suppl. Mat

References in corpus (12)

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• Scanning tunneling spectroscopy of superconducting LiFeAs single crystals: Evidence for two nodeless energy gaps and coupling to a bosonic mode
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Cited by in corpus (13)

• Fermion-boson many-body interplay in a frustrated kagome paramagnet
• Quasiparticle Interference and Strong Electron-Mode Coupling in the Quasi-One-Dimensional Bands of Sr${}_2$RuO${}_4$
• Imaging the Real Space Structure of the Spin Fluctuations in an Iron-based superconductor
• Unconventional pairing in single FeSe layers
• Orbital selectivity of layer resolved tunneling on iron superconductor Ba0.6K0.4Fe2As2
• Constraints on the total coupling strength to bosons in iron based superconductors
• Orbital-Selective High-Temperature Cooper Pairing Developed in the Two-Dimensional Limit
• Spectroscopic evidence of nematic fluctuations in LiFeAs
• Tunneling spectroscopy of c-axis epitaxial cuprate junctions
• Proximity-induced collective modes in an unconventional superconductor heterostructure
• Signatures of Amorphous Shiba State in FeTe${}_{0.55}$Se${}_{0.45}$
• Bosonic excitation spectra of superconducting $\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{r}}_2\mathrm{CaC}{\mathrm{u}}_2{\mathrm{O}}_{8+\delta }$ and $\mathrm{YB}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{6+\mathrm{x}}$ extracted from scanning tunneling spectra
• Quasiparticle interference in LiFeAs: Signature of inelastic tunneling through spin fluctuations