Giant exciton Mott density in anatase TiO2

TL;DR

This study combines advanced theoretical and ultrafast spectroscopy techniques to determine the highest exciton Mott density in anatase TiO2, revealing insights into exciton behavior in wide-gap insulators.

Contribution

It introduces a novel experimental approach to study high-density excitonic effects in ultraviolet-absorbing materials and reports the record-high Mott density in anatase TiO2.

Findings

Record-high exciton Mott density in anatase TiO2

Ultrafast ultraviolet spectroscopy reveals exciton-electron-hole interactions

Theoretical analysis supports experimental observations

Abstract

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.