Fluctuation and dimensionality effects on superconductivity in the BCS-BEC crossover regime

Hiroyuki Tajima, Ryo Hanai, Yoji Ohashi

Ryota Watanabe, Shunji Tsuchiya, Yoji Ohashi

Pinaki Majumdar, Sabyasachi Tarat

Kyosuke Adachi, Ryusuke Ikeda

The effects of superconducting fluctuation (SCF) on the thermodynamic properties of electron systems in the so-called BCS-BEC crossover regime are studied. As the attractive interaction between electrons becomes stronger upon approaching the BCS-BEC crossover regime, the importance of the mode coupling between SCF drastically increases. The enhanced mode coupling leads to lowering of both the zero-field superconducting critical temperature and the depairing field ${B}_{\text{c2}}(T)$. Consequently, SCF-induced contributions to the specific heat and the diamagnetic susceptibility can seemingly exceed the corresponding values in the Gaussian approximation. We discuss the relevance of the present results to the anomalous SCF-induced diamagnetic response observed in the iron selenide (FeSe).

Filippo Pascucci, Andrea Perali, Luca Salasnich

We calculate the parameters of the Ginzburg–Landau (GL) equation of a three-dimensional attractive Fermi gas around the superfluid critical temperature. We compare different levels of approximation throughout the Bardeen–Cooper–Schrieffer (BCS) to the Bose–Einstein Condensate (BEC) regime. We show that the inclusion of Gaussian fluctuations strongly modifies the values of the Ginzburg–Landau parameters approaching the BEC regime of the crossover. We investigate the reliability of the Ginzburg–Landau theory, with fluctuations, studying the behavior of the coherence length and of the critical rotational frequencies throughout the BCS-BEC crossover. The effect of the Gaussian fluctuations gives qualitative correct trends of the considered physical quantities from the BCS regime up to the unitary limit of the BCS-BEC crossover. Approaching the BEC regime, the Ginzburg–Landau equation with the inclusion of Gaussian fluctuations turns out to be unreliable.

Andrea Guidini, Luca Flammia, M. V. Miloševıć +1 more