Li Yi, Wu Congjun
Princeton Center for Theoretical Science, Princeton University, Princeton, NJ 08544, USA.
J Phys Condens Matter. 2014 Dec 10;26(49):493203. doi: 10.1088/0953-8984/26/49/493203. Epub 2014 Nov 17.
The rapid experimental progress of ultra-cold dipolar fermions opens up a whole new opportunity to investigate novel many-body physics of fermions. In this article, we review theoretical studies of the Fermi liquid theory and Cooper pairing instabilities of both electric and magnetic dipolar fermionic systems from the perspective of unconventional symmetries. When the electric dipole moments are aligned by the external electric field, their interactions exhibit the explicit d(r(2)-3z(2)) anisotropy. The Fermi liquid properties, including the single-particle spectra, thermodynamic susceptibilities and collective excitations, are all affected by this anisotropy. The electric dipolar interaction provides a mechanism for the unconventional spin triplet Cooper pairing, which is different from the usual spin-fluctuation mechanism in solids and the superfluid (3)He. Furthermore, the competition between pairing instabilities in the singlet and triplet channels gives rise to a novel time-reversal symmetry breaking superfluid state. Unlike electric dipole moments which are induced by electric fields and unquantized, magnetic dipole moments are intrinsic proportional to the hyperfine-spin operators with a Lande factor. Its effects even manifest in unpolarized systems exhibiting an isotropic but spin-orbit coupled nature. The resultant spin-orbit coupled Fermi liquid theory supports a collective sound mode exhibiting a topologically non-trivial spin distribution over the Fermi surface. It also leads to a novel p-wave spin triplet Cooper pairing state whose spin and orbital angular momentum are entangled to the total angular momentum J = 1 dubbed the J-triplet pairing. This J-triplet pairing phase is different from both the spin-orbit coupled (3)He-B phase with J = 0 and the spin-orbit decoupled (3)He-A phase.
超冷偶极费米子的快速实验进展为研究费米子新奇的多体物理开辟了全新的机遇。在本文中，我们从非常规对称性的角度综述了电偶极和磁偶极费米子系统的费米液体理论以及库珀对不稳定性的理论研究。当电偶极矩由外部电场排列时，它们的相互作用呈现出明确的d(r(2)-3z(2))各向异性。包括单粒子能谱、热力学磁化率和集体激发在内的费米液体性质均受此各向异性的影响。电偶极相互作用为非常规自旋三重态库珀对提供了一种机制，这与固体中通常的自旋涨落机制以及超流(3)He不同。此外，单重态和三重态通道中配对不稳定性之间的竞争产生了一种新奇的时间反演对称性破缺超流态。与由电场诱导且未量子化的电偶极矩不同，磁偶极矩是与朗德因子成正比的内禀量，与超精细自旋算符相关。其效应甚至在呈现各向同性但自旋轨道耦合性质的非极化系统中也有体现。由此产生的自旋轨道耦合费米液体理论支持一种集体声模，该声模在费米面上方呈现拓扑非平凡的自旋分布。它还导致了一种新奇的p波自旋三重态库珀对态，其自旋和轨道角动量与总角动量J = 1纠缠，称为J三重态配对。这个J三重态配对相既不同于J = 0的自旋轨道耦合(3)He-B相，也不同于自旋轨道解耦的(3)He-A相。
