We calculate the spin and density susceptibility of Weyl fermions with repulsive S-wave interaction in ultracold gases. Weyl fermions have a linear dispersion, which is qualitatively different from the parabolic dispersion of conventional materials. We find that there are different collective modes for the different strengths of repulsive interaction by solving the poles equations of the susceptibility in the random-phase approximation. In the long-wavelength limit, the sound velocity and the energy gaps vary with the different strengths of the interaction in the zero sound mode and the gapped modes, respectively. The particle–hole continuum is obtained as well, where the imaginary part of the susceptibility is nonzero.

我们计算了外尔费米子在超冷气体中具有排斥性 S 波相互作用的自旋和密度磁化率。外尔费米子具有线性色散，这与常规材料的抛物线色散有质的区别。通过求解随机相位近似中磁化率的极点方程，我们发现对于不同强度的排斥相互作用存在不同的集体模式。在长波长极限下，声速和能隙分别随着零声模和间隙模相互作用强度的不同而变化。还获得了粒子-空穴连续统，其中磁化率的虚部不为零。