Department of Physics, Columbia University, New York, New York 10027, USA.
Phys Rev Lett. 2011 Jan 28;106(4):046401. doi: 10.1103/PhysRevLett.106.046401. Epub 2011 Jan 25.
Significant excitonic effects were observed in graphene by measuring its optical conductivity in a broad spectral range including the two-dimensional π-band saddle-point singularities in the electronic structure. The strong electron-hole interactions manifest themselves in an asymmetric resonance peaked at 4.62 eV, which is redshifted by nearly 600 meV from the value predicted by ab initio GW calculations for the band-to-band transitions. The observed excitonic resonance is explained within a phenomenological model as a Fano interference of a strongly coupled excitonic state and a band continuum. Our experiment also showed a weak dependence of the excitonic resonance in few-layer graphene on layer thickness. This result reflects the effective cancellation of the increasingly screened repulsive electron-electron (e-e) and attractive electron-hole (e-h) interactions.
通过在包括二维π带鞍点奇点在内的宽光谱范围内测量其光学电导率，在石墨烯中观察到了显著的激子效应。强电子-空穴相互作用表现为在 4.62eV 处的不对称共振峰，其红移值接近从头计算 GW 计算预测的带间跃迁值的 600meV。观察到的激子共振可以在唯象模型中解释为强耦合激子态和能带连续体的 Fano 干涉。我们的实验还表明，少层石墨烯中激子共振对层厚度的依赖性较弱。这一结果反映了逐渐屏蔽的排斥电子-电子（e-e）和吸引电子-空穴（e-h）相互作用的有效抵消。
