Cooper pairs without “glue” in high-T _c superconductors: A universal phase diagram

Abstract

The phase diagram of high-Tc cuprates can be understood, without resorting to a boson mode, in terms of a single energy scale ∼ J, the antiferromagnetic (AF) exchange energy at the metal-insulator transition. As a result, holes form a new quantum object, the "pairon", i.e., a pair of holes localized within their local antiferromagnetic environment on the scale of the finite AF correlation length, ξAF . In the incoherent pseudogap phase, above Tc or within the vortex core, the pairon binding energies are distributed statistically, forming a "Cooper-pair glass". Contrary to conventional superconductors it is the mutual pair-pair interaction that is responsable for their condensation. We give a natural explanation for the ergodic rigidity of the excitation gap, the latter being constant with respect to a perturbation such as temperature or magnetic field, and determined only by the carrier concentration p and J.

Origin of the Fermi arcs in cuprates: a dual role of quasiparticle and pair excitations

“…In previous work we showed that this interaction follows the critical dome and has the value β ∼ 2 k B T c . Moreover, the pairon condensate model matches the phase diagram for a wide range of doping in terms of a single energy scale, J, the exchange energy [22]. Using the gap equation (9), and the energy bands k of cuprates from Markiewicz et al [26], the spectral function of quasiparticles is obtained for any wavevector k. Assuming nearly optimal doping (∆ p (0) = 40 meV, T c = 92 K) the spectral intensity in the AN direction crossing k F is shown in Fig.…”

“…In this article, we answer these questions in the framework of the condensation of preformed pairons [22]. To proceed, we calculate the spectral function for cuprates and directly compare the computed energy distribution curves (EDCs) to the ARPES measurements as a function of temperature and angle at the Fermi surface.…”

How ‘pairons’ are revealed in the electronic specific heat of cuprates

“…where p min ≈0.05 is the value at the SC onset and where C = 0.9 for Bi 2 Sr 2 CaCu 2 O 8+δ , as deduced from fits of tunneling data [20]. The critical doping p c ≈ 0.27 is directly related to the pairon size [20]. While the gap energy is analogous to the Cooper pairing between two fermions, the quantity β c arises from an additional four fermion term in the hamiltonian [22] which couples different pair states.…”

Model of charge triplets for high-T$_c$ cuprates

“…We emphasize the fundamental difference between such a local composite boson as a "preformed" pair and a Cooper pair composed of +k and -k partners. However, the on-site ZR boson also differs significantly from composite inter-site bosons, such as magnetic or lattice bipolarons [21,22] or magnetic "pairons" [23].…”