Zhang C X, Qiu X G
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, People's Republic of China.
J Phys Condens Matter. 2017 May 24;29(20):205701. doi: 10.1088/1361-648X/aa6804. Epub 2017 Mar 21.
Parity anomaly refers to the violation of coordinate reflection symmetry induced by the quantum fluctuations. It is proposed to exist in a graphene-like system with a finite bare mass for Dirac fermions, and manifests itself as a parity-violating quantum correction to the current of each species of fermions. Coulomb interaction greatly increases the fermion mass, and produces various types of excitons. Of particular interest is the ρ-exciton, which is directly connected to parity anomaly and can be generated by absorbing a specific photon. The exciton is a particle-hole bound state, and can be regarded as condensed-matter analogue of meson composed of quark-anti-quark pair. By virtue of this correspondence, we analyze the optical conductivity and calculate the mass of ρ-exciton by employing the Shifman-Vainshtein-Zakharov sum rule method that is widely used in the studies of hadron phenomenology. We show that ρ-exciton leads to a sharp peak in the optical conductivity, which is observable in optical experiments. Moreover, we study the impact of scalar-like excitons on two-photon processes by computing the decay amplitude, and also find peaks in the Raman spectra.
宇称反常是指由量子涨落引起的坐标反射对称性的破缺。它被认为存在于狄拉克费米子具有有限裸质量的类石墨烯系统中，并表现为对每种费米子电流的宇称破缺量子修正。库仑相互作用极大地增加了费米子质量，并产生各种类型的激子。特别令人感兴趣的是ρ激子，它与宇称反常直接相关，并且可以通过吸收特定光子产生。激子是一种粒子 - 空穴束缚态，可以被视为由夸克 - 反夸克对组成的介子的凝聚态类似物。借助这种对应关系，我们分析了光学电导率，并通过采用在强子现象学研究中广泛使用的希夫曼 - 瓦因施泰因 - 扎哈罗夫求和规则方法计算了ρ激子的质量。我们表明，ρ激子会导致光学电导率出现一个尖锐峰值，这在光学实验中是可观测到的。此外，我们通过计算衰变振幅研究了类标量激子对双光子过程的影响，并且在拉曼光谱中也发现了峰值。
