Superconducting Bose–Einstein condensates of Cooper pairs interacting with electrons

Ze Cheng

M. Casas, M. de Llano, A. Puente +2 more

M. Grether, MANUEL DE LLANO, S. RAMÍREZ +1 more

The role in superconductors of hole-Cooper-pairs (CPs) are examined and contrasted with the more familiar electron-CPs, with special emphasis on their “background” effect in enhancing superconducting transition temperatures Tc — even when electron-CPs drive the transition. Both kinds of CPs are, of course, present at all temperatures. An analogy is drawn between the hole CPs in any many-fermion system with the antibosons in a relativistic ideal Bose gas that appear in substantial numbers only at higher and higher temperatures. Their indispensable role in yielding a lower Helmholtz free energy equilibrium state is established. For superconductors, the problem is viewed in terms of a generalized Bose-Einstein condensation (GBEC) theory that is an extension of the Friedberg-T.D. Lee 1989 boson-fermion BEC theory of high-Tc superconductors in that the GBEC theory includes hole CPs as well as electron-CPs — thereby containing as well as further extending BCS theory to higher temperatures with the same weak-coupling electron-phonon interaction parameters. We show that the Helmholtz free energy of both 2e- and 2h-CP pure condensates has a positive second derivative, and are thus stable equilibrium states. Finally, it is conjectured that the role of hole pairs in ultra-cold fermionic atom gases will likely be negligible because the very low densities involved imply a “shallow” Fermi sea.

M.Á. De la Casa, J. Getino, MANUEL DE LLANO +1 more

Matt Mackie, Jyrki Piilo, Olavi Dannenberg

We theoretically examine the neutral atom-molecule analogue of the anomalous quantum correlations between degenerate electrons, i.e., Cooper pairs, that are responsible for superconductivity. Based on rogue dissociation of triatomic molecules (trimers) into opposite-momentum pairs of atoms and diatomic molecules (dimers) via a photoassociation or Feshbach resonance, we find a superfluid transition to a Bose-Einstein condensate of trimers dressed by atom-dimer Cooper pairs, at a critical temperature in reach of present ultracold technology.

F. Pistolesi, Giancarlo Calvanese Strinati

We argue that the natural variable to establish the crossover from Cooper-pair-based superconductivity to Bose-Einstein condensation of bound-electron pairs is the product ${\mathit{k}}_{\mathit{F}}$\ensuremath{\xi} of Fermi electron wave vector times the coherence length for two-electron correlation, and that Cooper-pair-based superconductivity is stable against bosonization down to ${\mathit{k}}_{\mathit{F}}$\ensuremath{\xi}\ensuremath{\simeq}2\ensuremath{\pi}. We also propose that the experimental plot by Uemura et al., relating the superconducting temperature ${\mathit{T}}_{\mathit{c}}$ to the Fermi temperature ${\mathit{T}}_{\mathit{F}}$ for a variety of ``exotic'' as well as conventional superconductors, can be rationalized by correlating the ratio ${\mathit{T}}_{\mathit{c}}$/${\mathit{T}}_{\mathit{F}}$ to ${\mathit{k}}_{\mathit{F}}$\ensuremath{\xi}. It appears in this way that the high-${\mathit{T}}_{\mathit{c}}$ superconductors lie in the plot by Uemura et al. near the ``instability'' line ${\mathit{k}}_{\mathit{F}}$\ensuremath{\xi}=2\ensuremath{\pi}.