Global Phase Diagram in Three Orbital Hubbard Model with Antiferromagnetic Hund Coupling

Alkali-doped fullerides A₃C₆₀ have been intensively investigated as a group of compounds exhibiting high-Tc superconductivity. Recently, the possibility of the Jahn-Teller (JT) metal state was suggested experimentally in Rb_xCs_3-xC₆₀ with a face-centered cubic structure [1]. The electronic structure of this material is considered to be described by a three orbital Hubbard model with the antiferromagnetic (AF) Hund coupling. From the theoretical point of view, a spontaneous orbital-selective Mott (SOSM) state where two orbitals are Mott-insulating but the other orbital remains metallic was proposed as a new quantum state emerging in the Hubbard model [2]. This state well reproduces the properties of the JT metal realized in the Alkali-doped fullerides. Motivated by the studies, we have analyzed the ordered states of the three-orbital model with the AF Hund coupling using the dynamical mean field theory and the continuous time quantum Monte Carlo method. As a result, two different phase diagrams were obtained depending on the presence or absence of geometrical frustration. We discuss the stability and competition of quantum states such as the superconducting and SOSM states.
[1] R.H.Zadik et al., Sci. Adv. 1, e1500059(2015).
[2] S.Hoshino, P.Werner, Phys. Rev. Lett. 118, 177002(2017).