Ultrafast optical spectroscopy of the lowest energy excitations in the Mott insulator compound YVO3: Evidence for Hubbard-type excitons

Abstract

Revealing the nature of charge excitations in strongly correlated electron systems is crucial to understanding their exotic properties. Here we use broadband ultrafast pump-probe spectroscopy in the visible range to study low-energy transitions across the Mott-Hubbard gap in the orbitally ordered insulator YVO 3 . Separating thermal and nonthermal contributions to the optical transients, we show that the total spectral weight of the two lowest peaks is conserved, demonstrating that both excitations correspond to the same multiplet. The pump-induced transfer of spectral weight between the two peaks reveals that the low-energy one is a Hubbard exciton, i.e., a resonance or a nearly bound state between a doublon and a holon. Finally, we speculate that the pump-driven spin disorder can be used to quantify the kinetic energy gain of the excitons in a ferromagnetic environment.

Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system

“…We obtain the equilibrium reflectivity R(o) from the measured ellipsometry data between 1 and 3.2 eV and from the literature outside of this range 6,42 . We perform a Drude-Lorentz fit 43,44 of the broadband equilibrium reflectivity over a wide energy range, from a few meV up to several tens of eV. We calculate the real and imaginary parts of the equilibrium dielectric function, e 1 (o) and e 2 (o), in the entire energy range through the KK relations 45 .…”

Mechanism of ultrafast relaxation of a photo-carrier in antiferromagnetic spin background

“…Distinguishing different elementary excitations in time domain therefore represents one of the major goals of the present research of nonequilibirum many-body systems. In this context, a rapid development of time-resolved experiments in condensed-matter systems [1][2][3][4][5][6][7] and cold atomic gases [8] provide both a challenge for theory as well as a testbed for new ideas. A large body of current theoretical research is based on studies of Hubbard-like models far from equilibrium, and it focuses both on relaxation dynamics after a sudden quench [9][10][11][12][13] and steadystate properties as a consequence of constant driving [14][15][16][17][18][19][20][21][22][23][24][25][26].…”

Speed limit of the insulator–metal transition in magnetite

“…[20] (see supplementary information) using an amplified Ti:sapphire laser system with ~80 fs pulse duration operating at 250 kHz. 800 nm pump and 500-800 nm probe beams were focused to spot diameters of ~110 and 90 µm, respectively.…”

“…We utilize time-resolved x-ray diffraction [18] and optical reflectivity [19,20] to disentangle the lattice and electronic degrees of freedom and study the role of phase separation in the Verwey transition. Starting from the insulating phase at 80 K, energy is rapidly injected into the electronic system via femtosecond (fs) laser excitation.…”