Superconductivity in Systems with Diluted Interactions

Maria N. Gastiasoro, Andrey V. Chubukov, Rafael M. Fernandes

F. Marsiglio, J. E. Hirsch

E.J. Calegari, José Jesús Rodríguez-Núñez

Yasutami Takada

We investigate the possibility of superconductivity and estimate the transition temperature ${T}_{c}$ in a system in which the bare electron-electron interaction $V(q)$ is arbitrary but basically repulsive. We employ the recently developed variational method which is believed to be the best one for the purpose at present. Through this study, we consider a concept of the Cooper pair originating not from an attractive but rather a repulsive bare potential. We find a special form for $V(q)$ to obtain ${T}_{c}$ over 200 K in the dilute electron-gas system. We discuss the band structure near the Fermi surface to produce such $V(q)'\mathrm{s}$ and propose a new exciton mechanism.

D. A. Kirzhnits

Johannes Kombe, Jean-Sébastien Bernier, Michael Köhl +1 more

We investigate the nonequilibrium behavior of dilute, attractively interacting Fermi gases subjected to finite-duration ramps of their internal interaction strength. We identify three dynamical regimes as a function of ramp duration using a time-dependent version of the Bardeen-Cooper-Schrieffer theory of superconductivity to model these systems. For short ramp durations, these systems become nonsuperconducting; however, fermions with opposite momenta remain paired albeit with reduced amplitudes, and the associated pair amplitude distribution is nonthermal. In this first regime, the disappearance of superconductivity is due to the loss of phase coherence between pairs. By contrast, for intermediate ramp durations, superconductivity survives but the magnitude of the order parameter is reduced and presents long-lived oscillations. Finally, for long ramp durations, phase coherence is almost fully retained during the finite-duration interaction quench, and the steady state is characterized by a thermal-like pair amplitude distribution. Using this approach, one can therefore dynamically tune the coherence between pairs to control the magnitude of the superconducting order parameter and even engineer a nonequilibrium state made of preformed pairs.