论文标题
腔中U（1） - 对称激子绝缘子的集体激发
Collective excitations of the U(1)-symmetric exciton insulator in a cavity
论文作者
论文摘要
我们研究了Fabry-Pérot腔中激素绝缘子（EI）的平衡状态和集体模式。在EI中，由于电子和孔之间的库仑相互作用，两个半导体或半学的频段自发杂交，导致间隙的打开。与电磁场的耦合将系统旋转相对于激子订单参数的相位旋转从$ u（1）$减少到$ z_2 $。虽然对离散对称性的还原通常会导致相位模式并增强有序相的稳定性，但与腔的耦合使平均场基地面状态不受影响。尽管腔体施加了较低的$ z_2 $对称性，但它的能量仍然在$ u（1）$相位旋转下仍然不变。在偶极仪中，可以追溯到线性光耦合的平衡和以零频率下的偶极自我相互作用。但是，在非零频率下，集体激发确实反映了较低的$ z_2 $对称性，这表明超出平均场外的波动可能在在有限温度下找到真实阶段起着至关重要的作用。
We investigate the equilibrium state and the collective modes of an excitonic insulator (EI) in a Fabry-Pérot cavity. In an EI, two bands of a semiconductor or semimetal spontaneously hybridize due to the Coulomb interaction between electrons and holes, leading to the opening of a gap. The coupling to the electromagnetic field reduces the symmetry of the system with respect to phase rotations of the excitonic order parameter from $U(1)$ to $Z_2$. While the reduction to a discrete symmetry would in general lead to a gapped phase mode and enhance the stability of the ordered phase, the coupling to the cavity leaves the mean-field ground state unaffected. Its energy remains invariant under $U(1)$ phase rotations, in spite of the lower $Z_2$ symmetry imposed by the cavity. In dipolar gauge, this can be traced back to the balancing of the linear light-matter coupling and the dipolar self-interaction at zero frequency. At nonzero frequency, however, the collective excitations do reflect the lower $Z_2$ symmetry, which shows that fluctuations beyond mean-field could play a crucial role in finding the true phase at finite temperature.
