Anomalous excitons and screenings unveiling strong electronic correlations in SrTi$_{1-x}$Nb$_x$O$_3$, 0$\leq$x$\leq$0.005

TL;DR

This study uncovers anomalous excitons in SrTiO3 caused by strong electron interactions, with their properties influenced by doping and temperature, revealing new insights into correlated electron phenomena.

Contribution

It provides the first observation and detailed analysis of anomalous excitons in SrTiO3, supported by ab initio calculations, highlighting the role of electron interactions in these phenomena.

Findings

Identification of anomalous excitons at specific energies in SrTiO3

Strong electron-electron and electron-hole interactions influence exciton properties

Doping and temperature affect exciton energy and spectral weight

Abstract

Electron-electron (e-e) and electron-hole (e-h) interactions are often associated with many exotic phenomena in correlated electron systems. Here, we report an observation of anomalous excitons at 3.75 , 4.67 and 6.11 eV at 4.2 K in bulk-SrTiO$_3$. Fully supported by ab initio GW Bethe-Salpeter equation calculations, these excitons are due to surprisingly strong e-h and e-e interactions with different characters: 4.67 and 6.11 eV are resonant excitons and 3.75 eV is a bound Wannier-like exciton with an unexpectedly higher level of delocalization. Measurements and calculations on SrTi$_{1-x}$Nb$_x$O$_3$ for 0.0001$\leq$x$\leq$0.005 further show that energy and spectral-weight of the excitonic peaks vary as a function of electron doping (x) and temperature, which are attributed to screening effects. Our results show the importance of e-h and e-e interactions yielding to anomalous excitons and thus bring out a new fundamental perspective in SrTiO$_3$.