Ultrafast transient absorption spectroscopy of strongly correlated Mott insulators*

We applied time-resolved transient absorption spectroscopy to systematically investigate the ultrafast optical responses of condensed matter systems. Under an intense pump pulse, absorption spectra indicate that the noninteracting electrons of band insulators produce a field-induced redshift, known as the dynamical Franz-Keldysh effect, as commonly expected. In contrast to band insulators, in Mott insulators, unconventional spectra are observed which do not fully reflect the dynamical Franz-Keldysh effect. While the spectra still exhibit fishbonelike structures mimicking the dynamical Franz-Keldysh effect, they show a negative difference absorption below the band edge, rendering a blueshift. In addition, the decomposed calculation reveals that the negative difference absorption is mainly contributed from the creation and the annihilation of transient double occupancy, implying that the unconventional spectra are purely driven by the electron correlations. These demonstrated unconventional responses can guide us to better understanding of the correlation-originated ultrafast electron dynamics in condensed matter systems.