Superconductivity and the Jahn–Teller Polaron

Abstract

In this article, we review the essential properties of high-temperature superconducting cuprates, which are unconventional isotope effects, heterogeneity, and lattice responses. Since their discovery was based on ideas stemming from Jahn–Teller polarons, their special role, together with the Jahn–Teller effect itself, is discussed in greater detail. We conclude that the underlying physics of cuprates cannot stem from purely electronic mechanisms, but that the intricate interaction between lattice and charge is at its origin.

Theoretical Possibilities for Flat Band Superconductivity

“…For the cuprates specifically, effects of hydrostatic and uniaxial pressure for multi-band models [1] or microstrains [27] have also been discussed. For attractively interacting two-band systems, the effects of the second band have been studied with Nozières-Schmitt-Rink formalism [28], BCS pairing Hamiltonian [29], and/or in the context of the BCS-BEC crossover [30] or Lifshitz transitions [31]. Thus a future problem is how these would apply to the flat-band cases.…”

High Temperature Superconductivity Arising in a Metal Sheet Full of Holes

“…The necessity of the slow rate especially for the temperature range of 20-60 K may be related to oxygen already absorbed in the PnM sample, which is known to undergo an antiferromagnetic transition below 54 K and to change its solid structure (β ⇆ γ phase) at 43 K. If the oxygen transformation truly happens in the PnM, the Jahn-Teller theorem may have to be considered as another glue for the 2D phonon-electron interaction, besides phonon engineering. The central issue of the theorem is that ionic displacements and electronic motion cannot be decoupled 34 . That is, the theorem is very compatible with the lowering of electronic kinetic energy Eq.…”

Meeting and Working with K. Alex Müller: Personal Memories

“…In addition to the OIEs on the superconducting transition temperature T c , the magnetic penetration depth λ ab (superfluid density) and the "pseudogap" temperature (charge-stripe ordering temperature) T * discussed above, we have also observed OIE's on several other physical quantities of cuprates such as the spin glass temperature T g [53,54], the Néel temperature T N [54], the spin-stripe ordering temperature T so [55] and the superconducting gap ∆ 0 [56]. All these studies give a consistent picture that the superconducting charge carriers in the cuprates have a polaronic character and that local lattice deformations play an important role in understanding these materials, as outlined in several review papers (see, e.g., [4,[35][36][37][38]57]). From the very beginning of the discovery of high-temperature superconductivity, Alex has pointed out that the cuprates exhibit microscopic inhomogeneities that are not due to poor sample preparation, but are an intrinsic property of the cuprates that is central to understanding the physical properties of these materials.…”