A tale of two metals: contrasting criticalities in the pnictides and hole-doped cuprates

Abstract

The iron-based high temperature superconductors share a number of similarities with their copper-based counterparts, such as reduced dimensionality, proximity to states of competing order, and a critical role for 3d electron orbitals. Their respective temperature-doping phase diagrams also contain certain commonalities that have led to claims that the metallic and superconducting (SC) properties of both families are governed by their proximity to a quantum critical point (QCP) located inside the SC dome. In this review, we critically examine these claims and highlight significant differences in the bulk physical properties of both systems. While there is now a large body of evidence supporting the presence of a (magnetic) QCP in the iron pnictides, the situation in the cuprates is much less apparent, at least for the end point of the pseudogap phase. We argue that the opening of the normal state pseudogap in cuprates, so often tied to a putative QCP, arises from a momentum-dependent breakdown of quasiparticle coherence that sets in at much higher doping levels but which is driven by the proximity to the Mott insulating state at half filling. Finally, we present a new scenario for the cuprates in which this loss of quasiparticle integrity and its evolution with momentum, temperature and doping plays a key role in shaping the resultant phase diagram.

Low-energy antiferromagnetic spin fluctuations limit the coherent superconducting gap in cuprates

“…Hence, our results provide evidence against a generic antiferromagnetic quantum critical point in cuprates. Instead, evidence points to a crossover with p from stronger to weaker correlations [6,33]. While subtracting the high-temperature phonon contribution does a reasonably good job of isolating the magnetic response, the differences between χ (ω) below and near T c , as shown in Fig.…”

Possible room-temperature signatures of unconventional 4f -electron quantum criticality in YbMn6Ge6−xSnEichenberger1, Magnette2, Malterre3 et al. 2020Phys. Rev. B91270View full textAdd to dashboardCite

“…In metals, such effects result in strong deviations from the Fermi-liquid behavior or unconventional superconductivity for instance [2,3]. Quantum criticality is being investigated in various materials including high-T c superconductors, insulating magnets, or heavy-fermion systems [1,4]. The latter are mainly Yb-or Ce-based intermetallics where low-energy scales give access to the QCP using nonthermal control parameters such as chemical doping, pressure, and magnetic field [2,3].…”

Phonon-mediated superconductivity in strongly correlated electron systems: A Luttinger–Ward functional approach

“…In what follows we provide a largely incomplete list of past and contemporary research subfields in the realm of superconductivity: i) Unconventional superconductors. Huge efforts have been devoted to investigate unconventional superconductivity [17][18][19][20][21][22][23][24][25], i.e. superconductivity unrelated to EPIs but arising from other pairing glues, originating microscopically solely from repulsive electron-electron interactions (EEIs).…”