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International Journal of Chemical Sciences

Study of BCS-BEC Crossover Physics and Evaluation of Energy Gap Parameters and Chemical Potential from BCS-Theory

Lekha Singh, L. K. Mishra

Published Jan 1, 2011• 0 citations
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Abstract

Using the theoretical formalism of C. Regal et al. PRL (2004), we have studied the BCS-BEC crossover regime. We have evaluated the value of energy gap parameter and chemical potential for the crossover as a function of dimensionless parameters |KF as| -1 from BCS-theory. Our theoretical result indicates that the crossover occurs in the very small region of the parameter-1< |KF as| -1 < 1.

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Using the theoretical formalism of T. H. Johnson etal.[PRL,116,240403 (2016)], Y. Nishida [PRL 114, 115302 (2015)], W. Yi and X. Chi[Phys.Rev. A92, 013623 (2015)] and A. Sindona etal.[PRL 111, 165303 (2013)], we have theoretically evaluated the dynamic structure factor (DSF) and spectral density of Fermi super fluid along BCS-BEC crossover regime.The evaluation is based on a model in which an impurity atom is trapped by an anharmonic potential with attractive interaction.We have evaluated impurity decay rate 4 (10 ) F E   as a function of vibrational energy A F E  for BCS limit ( 1 Fs ka =-0.5), unitarity limit ( 1 Fs ka =0.0) and BEC limit ( 1 Fs ka =1.0) respectively.Our theoretically obtained results show that
Superconductivity in iron-based, magnesium diborides, and other novel superconducting materials has a strong multi-band and multi-gap character. Recent experiments support the possibillity for a BCS-BEC crossover induced by strong-coupling and proximity of the chemical potential to the band edge of one of the bands. Here we study the simplest theoretical model which accounts for the BCS-BEC crossover in a two-band superconductor, considering tunable interactions and tunable energy separations between the bands. Mean-field results for condensate fraction, correlation length, and superconducting gap are reported in typical crossover diagrams to locate the boundaries of the BCS, crossover, and BEC regimes. When the superconducting gap is of the order of the local chemical potential, superconductivity is in the crossover regime of the BCS-BEC crossover and the Fermi surface of the small band is smeared by the gap opening. In this situation, small and large Cooper pairs coexist in the total condensate, which is the optimal condition for high-Tc superconductivity. The ratio between the gap and the Fermi energy in a given band results to be the best detection parameter for experiments to locate the system in the BCS-BEC crossover. Using available experimental data, our analysis shows that iron-based superconductors have the partial condensate of the small Fermi surface in the crossover regime of the BCS-BEC crossover, supporting the recent ARPES findings.