A common thread: The pairing interaction for unconventional superconductors

Abstract

The structures, the phase diagrams, and the appearance of a neutron resonance signaling an unconventional superconducting state provide phenomenological evidence relating the cuprates, the Fe-pnictides and chalcogenides as well as some heavy-fermion and actinide materials. Single-band and multiband Hubbard models have been found to describe a number of the observed properties of these materials so that it is reasonable to examine the origin of the pairing interaction in these models. In this review, based on the experimental phenomenology and studies of the pairing interaction for Hubbard-like models, it is proposed that spin-fluctuation mediated pairing is the common thread linking a broad class of superconducting materials.

Spin and charge excitations in artificial hole- and electron-doped infinite layer cuprate superconductors

“…Paramagnons have also been observed in the prototypical electron-doped (e-doped) cuprate compound Nd 2−x Ce x CuO 4 (NCCO) 11,12 . These findings have triggered several works 7,[13][14][15] , aiming to show that paramagnons are the driving excitations in Cooper pair formation. However there is no obvious correlation between the critical temperature (T c ) and the paramagnon energy, and this may indicate that also other low energy excitations play a role, such as phonons (via electron-phonon coupling) and charge modes 11,12,16 .…”

Study on Unconventional Superconductivity after the BCS Paradigm

“…[25] For a system with very good Fermi surface nesting, the electronic system will be instable to some long range ordered state, such as the charge-density-wave (CDW) or the spin-density-wave (SDW) state. In the iron based systems, the perfect nesting between the hole and electron pockets may just satisfy this situation leading to the formation of a long range SDW order in the parent phase in most families.…”

“…This resonance peak with a typical energy Ω ≤ 2∆ s can be detected with inelastic neutron scattering experiment and has been observed in cuprates, [34] Heavy Fermion [35] and recently in the iron pnictide superconductors. [36] This resonance peak may be understood as due to the spin flipping scattering when exciting a quasiparticle from the k to k + q with the pairing gap with the opposite signs, since in this case the BCS coherence factor is given by [25,31] …”

Properties of an almost localized Fermi liquid in an applied magnetic field revisited: a statistically consistent Gutzwiller approach

“…Fig.1 for visualization of such state). Within this model, not only the principal predictions of the Landau Fermiliquid theory have been derived [9,12], but also a unique explanation of the correlationdriven Mott metal-insulator transition [7] and the emergence of d-wave pairing have been discussed [13]. Importance of the Hubbard model manifests itself also as the basis of derivation of the so-called t − J model, which turned out to be very successful in description of the high temperature superconductivity in the cuprates (cf.…”