Palmieri Tania, Baldini Edoardo, Steinhoff Alexander, Akrap Ana, Kollár Márton, Horváth Endre, Forró László, Jahnke Frank, Chergui Majed
Laboratory of Ultrafast Spectroscopy, Lausanne Centre for Ultrafast Science (LACUS), Institute of Chemistry and Chemical Engineering (ISIC), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland.
Semiconductor Theory Group, Institute for Theoretical Physics, University of Bremen, Otto-Hahn-Alle 1, P.O. Box 330440, Bremen, Germany.
Nat Commun. 2020 Feb 12;11(1):850. doi: 10.1038/s41467-020-14683-5.
In a seminal paper, Mahan predicted that excitonic bound states can still exist in a semiconductor at electron-hole densities above the insulator-to-metal Mott transition. However, no clear evidence for this exotic quasiparticle, dubbed Mahan exciton, exists to date at room temperature. In this work, we combine ultrafast broadband optical spectroscopy and advanced many-body calculations to reveal that organic-inorganic lead-bromide perovskites host Mahan excitons at room temperature. Persistence of the Wannier exciton peak and the enhancement of the above-bandgap absorption are observed at all achievable photoexcitation densities, well above the Mott density. This is supported by the solution of the semiconductor Bloch equations, which confirms that no sharp transition between the insulating and conductive phase occurs. Our results demonstrate the robustness of the bound states in a regime where exciton dissociation is otherwise expected, and offer promising perspectives in fundamental physics and in room-temperature applications involving high densities of charge carriers.
在一篇具有开创性的论文中，马汉预测，在电子 - 空穴密度高于绝缘体 - 金属莫特转变时，半导体中仍可存在激子束缚态。然而，迄今为止，在室温下尚未有关于这种被称为马汉激子的奇异准粒子的确切证据。在这项工作中，我们结合超快宽带光谱学和先进的多体计算，揭示出有机 - 无机溴化铅钙钛矿在室温下存在马汉激子。在所有可实现的光激发密度下，即在远高于莫特密度的情况下，均观察到了万尼尔激子峰的持续存在以及带隙以上吸收的增强。这得到了半导体布洛赫方程解的支持，该解证实了绝缘相和导电相之间不存在尖锐的转变。我们的结果证明了在原本预期激子会解离的区域中束缚态的稳健性，并为基础物理学以及涉及高电荷载流子密度的室温应用提供了有前景的展望。
