Unravelling a new many-body large-hole polaron in a transition metal oxide that promotes high photocatalytic activity
npg Asia Materials Nature Research 14:1 (2022) 19
Authors:
Xiao Chi, Lily Mandal, Cuibo Liu, Angga Dito Fauzi, Anindita Chaudhuri, Thomas J Whitcher, Hariom Kirit Jani, Zhongxin Chen, Shibo Xi, Caozheng Diao, Muhammad Avicenna Naradipa, Xiaojiang Yu, Ping Yang, Antonio Helio Castro-Neto, Mark BH Breese, Kian Ping Loh, Thirumalai Venky Venkatesan, Andrivo Rusydi
Abstract:
In this work we investigate the delocalized excitons and excitons trapped by
a polaron formation in \BVO{} by means of resonant Raman spectroscopy. We
record Raman spectra with 16 laser lines between 1.9 and \SI{2.6}{\eV} and
analyze intensity variations of the Raman peaks for different vibrational
modes. The resonant Raman cross sections of the \Ag{} modes contain two types
of resonances. The first high-energy resonance near \SI{2.45}{\eV} belongs to a
transition between delocalized states; it is close to absorption edge measured
at \SI{2.3}{\eV} and exhibits a characteristic \SI{50}{\meV} anisotropy between
polarization parallel and perpendicular to the $c$ axis. The high energy Raman
resonance occurs inside the gap at \SI{1.94}{\eV} for all crystallographic
directions.
The in-gap resonance can involve a localized transition. We attribute it to
an exciton-polaron, formed by a small localized electron polaron of Holstein
type and delocalized holes. It manifests in the vibrations of vanadium and
oxygen atoms where polaron localization occurs and the resonance energy matches
theoretical predictions. The vibrational modes couple to the polaron with
different efficiency determined from resonant Raman profiles.Comment: main: 8 pages, 4 figures, supporting: 4 pages, 3 figure
