Photogenerated holon-doublon cluster states in strongly correlated low-dimensional electron systems

Abstract

We theoretically investigate the properties of multiphoton excited states in strongly correlated onedimensional ͑1D͒ and two-dimensional ͑2D͒ electron systems at half filling using the extended Hubbard model. In the 2D case, we find the photoexcited states where two or more than two holons and doublons are strongly bound, and the cluster of bound holons and doublons coexists with the surrounding antiferromagnetic ͑AF͒ spin order, for the realistic Coulomb interaction parameters. The holon-doublon cluster ͑HDC͒ states have a unique charge aggregation mechanism originating from the spin-spin interaction in the AF spin background as well as from the direct Coulomb interaction. In the 1D case, the HDC states are destabilized by the spin-spin interaction in contrast to the 2D case. These charge aggregation mechanisms are the outcomes of exotic natures of holons and doublons, and the difference in the mechanism between the 1D and 2D cases is due to the difference in the coupling between spin and charge degrees of freedom. We also calculate the light-induced absorption that enables us to experimentally observe the predicted HDC states.

Photocurrent suppression near antiferromagnetic transition in an organic Mott-insulator β′-(BEDT-TTF)(TCNQ) crystal

“…Thus, the photocurrent is not detected. It is also reported that strongly bound HDCs will occur especially in a 2D system . This supports the existence of HDCs in BEDT‐TTF layers because they have a 2D electronic state.…”

“…As one of the likeliest candidates underlying these mechanisms, we have considered the creation of strongly bound HDCs in 2D Mott insulators . The empty site (holon) and the doubly occupied site (doublon) are generated in the half‐filled Mott insulator with irradiation by light of sufficiently greater energy than the Hubbard gap.…”

“…Therefore, the holon and the doublon become enter a stable state as a holon–doublon pair (HDP). Further, HDPs generated by more than two holons and doublons form strongly bound clusters by the AF spin order in the AF state , in addition to the Coulomb interaction. The formation of HDCs suppresses the photogenerated carrier diffusion, and then, even if bias voltage is applied, it is difficult to extract the carrier from the HDC.…”

“…Recently, it was reported that the constraining effect between doubly occupied (doublon) and empty (holon) sites is important in explaining the metal–insulator transition in a Mott insulator . The concept of a doublon and holon instead of an excited electron and hole is used to describe the photoexcited states of the Mott insulator, and unique holon–doublon cluster (HDC) states are theoretically expected under the AF spin order .…”

Enhanced Charge Order in a Photoexcited One-Dimensional Strongly Correlated System

“…In this Letter we address the question of whether it is possible to reach other characteristically different states besides the metallic one after the photodoping. One possibility is the enhancement of charge-order when the attractive interaction between doublons and holons is incorporated [15]. We seek such enhancement in the extended half-filled 1D Hubbard model with an additional nearest-neighbor interaction.…”