Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 30123-970, Brazil.
Department of Physics, Chalmers University of Technology, 41296 Gothenburg, Sweden.
Nanoscale. 2023 Apr 13;15(15):7154-7163. doi: 10.1039/d2nr06732c.
The transition metal dichalcogenide family of semiconducting two-dimensional materials has recently shown a prominent potential to be an ideal platform to study the exciton Mott transition into electron-hole plasma and liquid phases due to their strong Coulomb interactions. Here, we show that pulsed laser excitation at high pump fluences can induce this exciton Mott transition to an electron-hole plasma in mono and few-layer transition metal dichalcogenides at room temperature. The formation of an electron-hole plasma leads to a broadband light emission spanning from the near infrared to the visible region. In agreement with our theoretical calculations, the photoluminescence emission at high energies displays an exponential decay that directly reflects the electronic temperature - a characteristic fingerprint of unbound electron-hole pair recombination. Furthermore, two-pulse excitation correlation measurements were performed to study the dynamics of electronic cooling, which shows two decay time components, one of less than 100 fs and a slower component of few ps associated with the electron-phonon and phonon-lattice bath thermalizations, respectively. Our work may shed light on further studies of the exciton Mott transition into other two-dimensional materials and their heterostructures and its applications in nanolasers and other optoelectronic devices.
过渡金属二卤族化合物半导体二维材料家族由于其强库仑相互作用，最近显示出作为研究激子 Mott 相变到电子-空穴等离子体和液相的理想平台的突出潜力。在这里，我们表明，在高泵浦强度下的脉冲激光激发可以在室温下将单原子层和少数层过渡金属二卤族化合物中的激子 Mott 相变诱导为电子-空穴等离子体。电子-空穴等离子体的形成导致宽带光发射，从近红外到可见光区域。与我们的理论计算一致，高能光致发光发射显示出指数衰减，直接反映了电子温度 - 这是未束缚电子-空穴对复合的特征指纹。此外，进行了双脉冲激发相关测量以研究电子冷却的动力学，其显示出两个衰减时间分量，一个小于 100 fs，另一个较慢的分量与电子-声子和声子-晶格浴热化分别相关。我们的工作可能为进一步研究激子 Mott 相变到其他二维材料及其异质结构以及其在纳米激光器和其他光电设备中的应用提供启示。
