Mott transitions in two-orbital Hubbard systems

Nils Blümer, C. Knecht, Krunoslav Požgajčić +1 more

昌久 古賀, Akihisa Koga

Akihisa Koga, Kensuke Inaba, Norio Kawakami

Evgeny A. Plekhanov, Adolfo Avella, Francesco Paolo Mancini +1 more

The orbital degrees of freedom are of vital importance in explanation of various phenomena. Among them is the orbital-selective Mott transition (OSMT), which is thought to occur in several materials as Ca 2− x Sr x RuO 4 and La n+1 Ni n O 3 n +1 . OSMT is usually studied in the infinite-dimension limit, and for the time being, it is not clear if it could survive in one-dimensional (1D) case. There exist two scenarios for the OSMT: upon increasing the interaction in a two-band system i) one of the bands becomes insulating, while the other remains metallic and ii) one of the bands becomes empty, while the other may eventually undergo a single-band Mott insulator transition. In this work, we present a preliminary study of the two-orbital Hubbard model by means of Density Matrix Renormalization Group in 1D at quarter-filling, where the second scenario seems to be realized. In particular, we study the orbital densities, double occupancies and form-factors also in the case of finite inter-orbital inter-site hopping.

Norio Kawakami, 川上 則雄

Satoru Odashima

Electronic states of the two-orbital Hubbard model are investigated by means of the composite opeator method. In addition to the transfer within the same kind of orbital, we introduce the off-diagonal transfer t ', which provides the mixing of orbitals. In the t ' = 0 case, the system shows the orbital selective Mott transition at U = 4. Upon adding t ', the band gap goes wider. This increase of the gap originates from the crossover between the Mott-insulator and the band-insulator.