Dynamical correlations and nonequilibrium sum rules in photodoped Hubbard ladders

TL;DR

This study uses matrix product state techniques to analyze the nonequilibrium dynamical response of a photodoped Hubbard ladder, revealing pump-direction-dependent spectral weight transfer and nonthermal metallic states.

Contribution

It introduces a combined spin-charge sum rule applicable out-of-equilibrium and demonstrates how optical pumping redistributes spectral weight in a strongly correlated ladder system.

Findings

Spectral weight is transferred from spin to charge responses below the Mott gap.

Pump direction influences the disruption of magnetic correlations.

The system becomes a nonthermal metallic state with gapless charge excitations.

Abstract

Using matrix product state techniques we study the nonequilibrium dynamical response of the half-filled Hubbard ladder when subject to an optical pump. Optical pumping offers a way of producing and manipulating new strongly correlated phenomena by suppressing existing magnetic correlations. The ladder allows the effects of pump directionality to be investigated, and compared to a single chain it has strong spin-charge coupling and a fully gapped excitation spectrum, promising different nonequilibrium physics. We compute time-dependent correlations, including the nonequilibrium dynamical structure factors for spin and charge. By deriving a combined spin-charge sum rule that applies both in and out-of-equilibrium, we show that spectral weight is pumped directly from the antiferromagnetic spin response into a low energy $\omega\sim 0$ charge response below the Mott gap. The transfer of weight is pump direction dependent: pumping directed along the legs disrupts magnetic correlations more than pumping in the rung direction, even if the post pump energy density is similar. The charge correlation length is dramatically enhanced by the pump, whilst the spin correlations are most strongly suppressed at nearest and next-nearest neighbour spacings. After the pump the system is in a nonthermal correlated metallic state, with gapless charge excitations and approximately equal spin and charge correlation lengths, emphasising the importance of treating these degrees of freedom on an equal footing in nonequilibrium systems.