Stabilization of vortex-liquid state by strong pairing interaction

Abstract

We theoretically investigate qualitative features of the field-temperature ($H$-$T$) phase diagram of superconductors with strong attractive interaction lying in the BCS-BEC crossover regime. Starting with a simple attractive Hubbard model, we estimate three kinds of characteristic fields, i.e., the pair-formation field $H^{\ast }$, the vortex-liquid-formation field $H_{c2}$, and the vortex-lattice-formation field $H_{\mathrm{melt}}$. The region between $H_{c2}$ and $H_{\mathrm{melt}}$, as well as that between $H_{c2}$ and $H^{\ast }$, is found to be enlarged as the interaction is stronger. In other words, a strong attractive interaction can stabilize both the vortex-liquid and preformed-pair regions. We also point out the expected particle-density dependence of the $H$-$T$ phase diagram.

14 pages, 7 figures