Baldini Edoardo, Palmieri Tania, Dominguez Adriel, Rubio Angel, Chergui Majed
Laboratory of Ultrafast Spectroscopy, ISIC and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Department of Physics, Massachusetts Institute of Technology, 02139 Cambridge, Massachusetts, USA.
Phys Rev Lett. 2020 Sep 11;125(11):116403. doi: 10.1103/PhysRevLett.125.116403.
Elucidating the carrier density at which strongly bound excitons dissociate into a plasma of uncorrelated electron-hole pairs is a central topic in the many-body physics of semiconductors. However, there is a lack of information on the high-density response of excitons absorbing in the near-to-mid ultraviolet, due to the absence of suitable experimental probes in this elusive spectral range. Here, we present a unique combination of many-body perturbation theory and state-of-the-art ultrafast broadband ultraviolet spectroscopy to unveil the interplay between the ultraviolet-absorbing two-dimensional excitons of anatase TiO_{2} and a sea of electron-hole pairs. We discover that the critical density for the exciton Mott transition in this material is the highest ever reported in semiconductors. These results deepen our knowledge of the exciton Mott transition and pave the route toward the investigation of the exciton phase diagram in a variety of wide-gap insulators.
阐明强束缚激子解离为不相关电子 - 空穴对等离子体时的载流子密度，是半导体多体物理学中的核心课题。然而，由于在这个难以捉摸的光谱范围内缺乏合适的实验探针，关于近紫外到中紫外吸收的激子的高密度响应信息不足。在此，我们展示了多体微扰理论与最先进的超快宽带紫外光谱学的独特结合，以揭示锐钛矿型TiO₂ 的紫外吸收二维激子与电子 - 空穴对海洋之间的相互作用。我们发现，这种材料中激子莫特转变的临界密度是半导体中报道过的最高值。这些结果加深了我们对激子莫特转变的认识，并为研究各种宽禁带绝缘体中的激子相图铺平了道路。
