Biexciton formation and exciton coherent coupling in layered GaSe
Biexciton formation and exciton coherent coupling in layered GaSe
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DOI：
10.1063/1.4917169
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发表时间：
2015-06-07
影响因子：
4.4
通讯作者：
Karaiskaj, D.
中科院分区：
文献类型：
--
作者：
Dey, P.;Paul, J.;Karaiskaj, D.
利用非线性二维傅里叶变换（2DFT）和线性吸收光谱技术研究了层状半导体GaSe中激子的电子结构和光学性质。在1s激子共振中，在吸收光谱中发现了两个峰，这两个峰是激子基态分裂成三重态和单重态的结果。从激发脉冲的共线偏振中获得的2DFT光谱具有一个额外的峰，源于单线态和三重态之间的相干能量转移。在激发脉冲的交叉线极化处，2DFT光谱暴露出一个可能来自束缚双激子的新峰。利用光学布洛赫方程对包含多体效应的四能级系统进行了模拟，很好地再现了偏振相关的2DFT光谱。虽然双激子效应被认为在这种材料中很强，但只能观察到束缚双激子产生的适度贡献。根据2DFT谱峰的分离，估计双激子的结合能约为2mev。温度依赖吸收和2DFT测量，结合声子光谱的“从头算”理论计算，表明与A(1)'声子模式有很强的相互作用。激发密度相关的2DFT测量揭示了激发诱导的失相，并提供了当前GaSe晶体中激子均匀线宽的下限。(C) 2015 AIP出版有限责任公司
Nonlinear two-dimensional Fourier transform (2DFT) and linear absorption spectroscopy are used to study the electronic structure and optical properties of excitons in the layered semiconductor GaSe. At the 1s exciton resonance, two peaks are identified in the absorption spectra, which are assigned to splitting of the exciton ground state into the triplet and singlet states. 2DFT spectra acquired for co-linear polarization of the excitation pulses feature an additional peak originating from coherent energy transfer between the singlet and triplet. At cross-linear polarization of the excitation pulses, the 2DFT spectra expose a new peak likely originating from bound biexcitons. The polarization dependent 2DFT spectra are well reproduced by simulations using the optical Bloch equations for a four level system, where many-body effects are included phenomenologically. Although biexciton effects are thought to be strong in this material, only moderate contributions from bound biexciton creation can be observed. The biexciton binding energy of similar to 2 meV was estimated from the separation of the peaks in the 2DFT spectra. Temperature dependent absorption and 2DFT measurements, combined with "ab initio" theoretical calculations of the phonon spectra, indicate strong interaction with the A(1)' phonon mode. Excitation density dependent 2DFT measurements reveal excitation induced dephasing and provide a lower limit for the homogeneous linewidth of the excitons in the present GaSe crystal. (C) 2015 AIP Publishing LLC.