Theory of photoinduced ultrafast switching to a spin-orbital ordered hidden phase

Abstract

Photo-induced hidden phases are often observed in materials with intertwined orders. Understanding the formation of these non-thermal phases is challenging and requires a resolution of the cooperative interplay between different orders on the ultra-short timescale. In this work, we demonstrate that non-equilibrium photo-excitations can induce a state with spin-orbital orders entirely different from the equilibrium state in the three-quarter-filled two-band Hubbard model. We identify a general mechanism governing the transition to the hidden state, which relies on a non-thermal partial melting of the intertwined orders mediated by photoinduced charge excitations in the presence of strong spin-orbital exchange interactions. Our study theoretically confirms the crucial role played by orbital degrees of freedom in the light-induced dynamics of strongly correlated materials and it shows that the switching to hidden states can be controlled already on the fs timescale of the electron dynamics.

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

“…These mechanisms lead to numerous competing metastable phases accessible via ultrafast photoexcitation. In recent years, several exciting scenarios for the ultrafast manipulation of ordered states have been reported, including possible high-temperature superconducting states in light-driven cuprates 3 , 4 and fullerides 5 , hidden states in 1T-TaS 2 6 , as well as photo-induced non-thermal magnetic and orbital-ordered states 7 , 8 . Less attention has been paid to the feedback mechanisms between the long-range electronic or magnetic ordering and the dynamics of the photoexcited charge carriers.…”

Influence of spin and orbital fluctuations on Mott-Hubbard exciton dynamics in LaVO3 thin films

“…Under what conditions do these excitons form, what are their characteristic timescales, and what degrees of freedom influence their dynamics? Advances in theory and experimental techniques have begun to address these questions, indicating for example that the recombination rates are proportional to the MH gap and mediated by magnon emission [11][12][13][14]. Ultrafast optical spectroscopy is a technique particularly well suited to furthering our understanding of this field, and has been used extensively to study ultrafast dynamics in many MH insulators, including cuprates [15][16][17], manganites [18,19], and TaS 2 [20].…”

Optical control of competing exchange interactions and coherent spin-charge coupling in two-orbital Mott insulators

“…Natural extension of this work are numerical studies for extended systems. This could be possible for example using multiband extensions of nonequilibrium Dynamical Mean Field Theory (DMFT) [48][49][50][51][52]. We emphasize that, besides the possibility to induce coherent charge dynamics, the presence of the spin-charge coupling should also be visible for short pulses, enabling the excitation of doubly ionized states which could remain coherent due to the gapping with the normal Mott-Hubbard gap.…”