Ye Fei, Chen Yan, Wang Z D, Zhang F C
Center for Advanced Study, Tsinghua University, Beijing 100084, People's Republic of China. Department of Physics and Center for Theoretical and Computational Physics, The University of Hong Kong, Hong Kong, People's Republic of China.
J Phys Condens Matter. 2009 Sep 2;21(35):355701. doi: 10.1088/0953-8984/21/35/355701. Epub 2009 Aug 10.
The imbalanced superfluid state of spin- 1/2 fermions with s-wave pairing is numerically studied by solving the Bogoliubov-de Gennes equation at zero temperature in an annular disk geometry with narrow radial width. Two distinct types of systems are considered. The first case may be relevant to heavy fermion superconductors, where magnetic field causes spin imbalance via Zeeman interaction and the system is studied in a grand canonical ensemble. As the magnetic field increases, the system is transformed from the uniform superfluid state to the Fulde-Ferrell-Larkin-Ovchinnikov state, and finally to the spin polarized normal state. The second case may be relevant to cold fermionic systems, where the number of fermions of each species is fixed as in a canonical ensemble. In this case, the ground state depends on the pairing strength. For weak pairing, the order parameter exhibits a periodic domain wall lattice pattern with a localized spin distribution at low spin imbalance, and a sinusoidally modulated pattern with extended spin distribution at high spin imbalance. For strong pairing, the phase separation between the superfluid state and polarized normal state is found to be preferable, while the increase of spin imbalance simply changes the ratio between them.
通过在具有窄径向宽度的环形盘几何结构中求解零温度下的博戈留波夫 - 德热纳方程，对具有s波配对的自旋 - 1/2费米子的不平衡超流态进行了数值研究。考虑了两种不同类型的系统。第一种情况可能与重费米子超导体有关，其中磁场通过塞曼相互作用导致自旋不平衡，并且该系统是在巨正则系综中进行研究的。随着磁场增加，系统从均匀超流态转变为富尔德 - 费雷尔 - 拉金 - 奥夫钦尼科夫态，最终转变为自旋极化正常态。第二种情况可能与冷费米子系统有关，其中每种费米子的数量如在正则系综中那样是固定的。在这种情况下，基态取决于配对强度。对于弱配对，序参量在低自旋不平衡时呈现具有局域自旋分布的周期性畴壁晶格图案，在高自旋不平衡时呈现具有扩展自旋分布的正弦调制图案。对于强配对，发现超流态和极化正常态之间的相分离是更可取的，而自旋不平衡的增加仅仅改变它们之间的比例。
