arXiv subjects

M. de Llano

Publications and source records attributed to M. de Llano.

40 records · Page 3Linked to original sources

arXiv2000

Linear to quadratic crossover of Cooper pair dispersion relation

Cooper pairing is studied in three dimensions to determine its binding energy for all coupling using a general separable interfermion interaction. Also considered are Cooper pairs (CPs) with nonzero center-of-mass momentum (CMM). A coupling-independent {\it linear} term in the CMM dominates the pair excitation energy in weak coupling and/or high fermion density, while the more familiar quadratic term prevails only in the extreme low-density (i.e., vacuum) limit for any nonzero coupling. The linear-to-quadratic crossover of the CP dispersion relation is analyzed numerically, and is expected to play a central role in a model of superconductivity (and superfluidity) simultaneously accommodating a BCS condensate as well as a Bose-Einstein condensate of CP bosons.

cond-mat.supr-con↗

arXiv2000

Low-dimensional BEC

The Bose-Einstein condensation (BEC) temperature $T_{c}$ of Cooper pairs (CPs) created from a very general interfermion interaction is determined for a {\it linear}, as well as the usual quadratic, energy {\it vs}% center-of-mass momentum dispersion relation. This $T_{c}$ is then compared to that of Wen & Kan (1988) in $d=2+ε$ dimensions, for small $ε$, in a geometry of an infinite stack of parallel (e.g., copper-oxygen) planes as in a cuprate, and with a new result for linear-dispersion CPs. This allows addressing, as a rough first approximation, superconductivity for any $d>1$.

cond-mat.supr-con↗

arXiv2000

Superconductivity as a Bose-Einstein condensation?

Bose-Einstein condensation (BEC) in two dimensions (2D) (e.g., to describe the quasi-2D cuprates) is suggested as the possible mechanism widely believed to underlie superconductivity in general. A crucial role is played by nonzero center-of-mass momentum Cooper pairs (CPs) usually neglected in BCS theory. Also vital is the unique {\it linear} dispersion relation appropriate to weakly-coupled "bosonic" CPs moving in the Fermi sea--rather than in vacuum where the dispersion would be quadratic but only for very strong coupling, and for which BEC is known to be impossible in 2D.

cond-mat.supr-con↗

arXiv1994

Exotic and conventional superconductivity in a Dirac supersymmetric scheme

A new pairing theory for many-fermion systems is obtained via the Dirac supersymmetry framework recently introduced to describe Dirac particles in external potentials. It is shown that the standard Bogoliubov-Valatin canonical transformation treatment of the quasi-particle BCS singlet pairing mechanism naturally falls within this framework. Straightforward generalizations in which the fermions can be ascribed $ ν$ {\it components} are shown to lead to enhanced gap energies and critical temperatures as in the case of cuprate superconductors without invoking a stronger electron-boson coupling. The new $T_{c}^{max}$ limit is $T_c^{max} = νT_c^{BCS}$, with $T_c^{BCS} \approx 40^0 K$.

cond-mat↗