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

TL;DR

This paper presents a theoretical framework explaining how ultrafast photoexcitation can induce a non-thermal, hidden spin-orbital ordered phase in strongly correlated materials, with potential control on femtosecond timescales.

Contribution

It introduces a general mechanism for photoinduced switching to hidden spin-orbital phases via non-thermal melting of intertwined orders in a Hubbard model.

Findings

Photoexcitation induces a hidden spin-orbital order different from equilibrium.

The transition is governed by non-thermal partial melting of intertwined orders.

Control of hidden state switching occurs on femtosecond timescales.

Abstract

Photoinduced 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 ultrashort 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.