Abstract:
Doping charge carriers into Mott insulators provides a pathway to produce intriguing emergent phenomena. In equilibrium systems, doping can be chemically controlled. On the other hand, photo-doping, where particles are excited across the Mott gap, provides an alternative way. Compared to chemical-doping, photo-doping creates a wider variety of carriers, which may lead to the emergence of fascinating nonequilibrium states. In particular, when the gap is large, the life-time of photo-carriers becomes exponentially enhanced, which can lead to a metastable states after the intraband cooling of photo-carriers occurs.
In this talk, we reveal the peculiar features of such metastable states realized in the one-dimensional extended Hubbard model [1,2]. Namely, we show that the corresponding wave function in the larger on-site interaction limit can be expressed as |Ψ⟩ = |Ψcharge⟩|Ψspin⟩|Ψη−spin⟩, which indicates the separation of spin, charge and η−spin degrees of freedoms. Here η−spin represents the type of the photo-carriers. This state is analogous to the Ogata-Shiba state of the doped Hubbard model in equilibrium. |Ψcharge⟩ is determined by spinless free fermions, |Ψspin⟩ by the isotropic Heisenberg model in the squeezed spin space, and |Ψη−spin⟩ by the XXZ model in the squeezed η-spin space. In the photo-doped system, one can find the metastable η-pairing and charge-density-wave (CDW) phases, which states to the gapless and gapful states of the XXZ model, respectively. The η-pairing phase hosts a quasi-long range order associated with the condensation of pairs with momentum π. The CDW phase is characterized by the string order as the Haldane phase. The specific form of the wave function allows us to accurately determine correlation functions, and suggests that the total central charge of the η-pairing state is 3 and that of the CDW state is 2. Our results demonstrate that the emergent degrees of freedom activated by photo-doping can lead to peculiar types of quantum liquids absent in equilibrium.
[1] Y. Murakami, S. Takayoshi, T. Kaneko, Z. Sun, D. Golež, A. J. Millis, P. Werner, Comm. Phys. 5, 23 (2022).
[2] Y. Murakami, S. Takayoshi, T. Kaneko, A. Läuchli, P. Werner, Phys. Rev. Lett. 130, 106501 (2023).