Dipole Transitions in the Hubbard Model

B. Sriram Shastry

Adrien-Isaac Bolens, アドリアン イザク ボロンス

Yunseok Seo, Geunho Song, Yong-Hui Qi +1 more

We show that the competition between the fermi liquidity and the gap generation, which is the physics of the Hubbard model, can be realized in a canonical holographic model of a fermion with bulk mass and a dipole interaction. The bulk mass near 1/2 tends to protect the fermi liquidity while large dipole coupling attempts to generate the mass gap so that the model is equipped with the basic mechanism of the Mott transition and expected to play the role of Hubbard model in holographic context. In fact, the spectral densities of the holographic model agree with the dynamical mean field theory (DMFT) calculation in two features: the 'three peaks' and 'the transfer' of the degree of freedom from the quasi-particle peak to the side peak. The phase diagram of our holographic model contains six phases including bad metals and pseudo-gap as well as the Fermi liquid and Mott insulator, and a line connecting the last two defines a Holographic version of Hubbard model. The experimental data for spectral densities of Vanadium Oxide materials seem to be well fit by our theory.

Assa Auerbach

J. Monecke

Yasuhiro Tanaka, Manabu Daira, Kenji Yonemitsu

Photoinduced dynamics in an excitonic insulator is studied theoretically by using a two-orbital Hubbard model on the square lattice where the excitonic phase in the ground state is characterized by the BCS-BEC crossover as a function of the interorbital Coulomb interaction. We consider the case where the order has a wave vector $\mathbit{Q}=(0,0)$ and photoexcitation is introduced by a dipole transition. Within the mean-field approximation, we show that the excitonic order can be enhanced by the photoexcitation when the system is initially in the BEC regime of the excitonic phase, whereas it is reduced if the system is initially in the BCS regime. The origin of this difference is discussed from behaviors of momentum distribution functions and momentum-dependent excitonic pair condensation. In particular, we show that the phases of the excitonic pair condensation have an important role in determining whether the excitonic order is enhanced or not.