What is the pairing glue in the cuprates? Insights from normal and anomalous propagators

Abstract

Both the pairing and the pair-breaking modes lead to similar kinks of the electron dispersion curves in superconductors, and therefore the photoemission spectroscopy can not be straightforwardly applied in search for their pairing glue. If the momentum-dependence of the normal and anomalous self-energy can be neglected, manipulation with the data does allow us to extract the gap function ∆(ω) and therefore also the pairing glue. However, in the superconducting cuprates such procedure may not be justified. In this paper we point out that the pairing glue is more directly visible in the spectral function of the Nambu-Gor'kov anomalous propagator and we demonstrate that this function is in principle experimentally observable.

Model-independent determination of the gap function of nearly localized superconductors

“…When interpreted within the extended Eliashberg theory, the features (i) and (ii) of ∆(ω) are consistent with a finite coupling of the electrons to a soft pair-breaking mode at ω * , see Fig. 1b in [13].…”

“…The scaling of T c with the distance from the critical point, the gap-to-T c ratio, the magnitude of the critical resistivity, etc., further help to identify the symptoms of the various mechanisms driving the QBS [1]. On the other hand, a comprehensive picture of the transition would be provided by the knowledge of the gap func-tion ∆(ω) which is known to carry information not only on the pairing glue [12], but also on the pair-breaking processes [13,14] which occur in a superconductor.…”

Odd-frequency superconductivity near a magnetic impurity in a conventional superconductor

“…As the impurity strength is increased from J m = 0 (panels (c), Further we note that the parity of the real and imaginary parts of any correlation are opposite. 58 The real part, being even in frequency, has the same sign between the YSR bound state energies (|ω| < ε 0 ) and changes sign as the frequency crosses the YSR bound state energies, vanishing at the gap edges (ε 0 < |ω| < ∆). The imaginary part, being odd in frequency, has sharp peaks around the YSR bound-state energies with opposite sign and spatial modulation determined by that of Fig.…”

Microscopic interpretation of the Dynes formula for the tunneling density of states

“…The first term is the spatially homogeneous pairing interaction, the second term is a fluctuating potential which is usually large in samples described by Eq. ( 1), and the last term is a much weaker classical pair-breaking field, polarized along a fixed direction in spin space [20]. We assume that the fields U and V are distributed according to independent and spatially uncorrelated even functions P s (U ) and P m (V ).…”