Asia Pacific Center for Theoretical Physics (APCTP), Pohang, Gyeongbuk, Korea.
Phys Rev Lett. 2011 Dec 30;107(27):270404. doi: 10.1103/PhysRevLett.107.270404. Epub 2011 Dec 29.
We investigate the energy band structure of the superfluid flow of ultracold dilute Fermi gases in a one-dimensional optical lattice along the BCS to Bose-Einstein condensate (BEC) crossover within a mean-field approach. In each side of the crossover region, a loop structure (swallowtail) appears in the Bloch energy band of the superfluid above a critical value of the interaction strength. The width of the swallowtail is largest near unitarity. Across the critical value of the interaction strength, the profiles of density and pairing field change more drastically in the BCS side than in the BEC side. It is found that along with the appearance of the swallowtail, there exists a narrow band in the quasiparticle energy spectrum close to the chemical potential, and the incompressibility of the Fermi gas consequently experiences a profound dip in the BCS side, unlike in the BEC side.
我们在平均场方法下研究了超冷稀费米气体在一维光学晶格中超流流动的能带结构，沿 BCS 到玻色-爱因斯坦凝聚（BEC）交叉区域。在交叉区域的每一侧，在相互作用强度的一个临界值之上，超流体的 Bloch 能带中出现了一个环结构（燕尾）。燕尾的宽度在近幺正性时最大。在相互作用强度的临界值处，在 BCS 侧，密度和配对场的分布比在 BEC 侧变化更为剧烈。结果发现，随着燕尾的出现，在准粒子能谱中靠近化学势处存在一个窄带，费米气体的不可压缩性在 BCS 侧经历了一个深刻的下降，而在 BEC 侧则没有。
