Study of the Hubbard model on the triangular lattice using dynamical cluster approximation and dual fermion methods

We investigate the Hubbard model on the triangular lattice at half-filling using the dynamical cluster approximation (DCA) and dual fermion (DF) methods in combination with continuous-time quantum Monte carlo (CT QMC) and semiclassical approximation (SCA) methods. We study the one-particle properties and nearest-neighbor spin correlations using the DCA method. We calculate the spectral functions using the CT QMC and SCA methods. The spectral function in the SCA and obtained by analytic continuation of the Pade approximation in CT QMC are in good agreement. We determine the metal-insulator transition (MIT) and the hysteresis associated with a first-order transition in the double occupancy and nearest-neighbor spin correlation functions as a function of temperature. As a further check, we employ the DF method and discuss the advantages and limitation of the dynamical mean field theory (DMFT), DCA and recently developed DF methods by comparing Green's functions. We find an enhancement of antiferromagnetic (AF) correlations and provide evidence for magnetically ordered phases by calculating the spin susceptibility.Comment: 6 pages, 7 figure

Interplay of disorder and interaction in the bilayer band-insulator : A Determinant Quantum Monte Carlo study

Earlier work [arXiv:1206.2407,arXiv:2206.06085] have shown the band insulator (BI) to superfluid (SF) phase transition in the half-filled bilayer attractive Hubbard model. In this paper we append the effects of random on-site disorder on the single particle properties and two particle pair-pair correlations in that model. Using the determinant quantum Monte Carlo simulation we observe that the on-site random disorder plays a significant role in the localization of on-site pairs, hence in the reduction of the effective hopping. This results in an increase of the double occupancy, which is an effect similiar to the attractive interaction. We find no change in the critical value of the interaction at which the model undergoes from BI to SF regime even though the pair-pair correlations get suppressed for finite on-site disorder strengths V_d/t=0.1-0.8. We also confirm that the weak disorder suppresses the SF phase largely in the strong-coupling limit. Hence the region of the SF phase reduces in the presence of random on-site disorder. Finally, through finite-size scaling we have estimated the critical disorder strength V_d^c/t~1.44 at |U|/t=5.Comment: 8 Pages, 9 Figure

Possible origin of the reduced magnetic moment in iron pnictides: A dynamical mean field theory study

We investigate the phase diagram of a two-band frustrated Hubbard model in the framework of dynamical mean field theory. While a first-order phase transition occurs from a paramagnetic (PM) metal to an antiferromagnetic (AF) insulator when both bands are equally frustrated, an intermediate AF metallic phase appears in each band at different $U_c$ values if only one of the two bands is frustrated, resulting in continuous orbital-selective phase transitions from PM metal to AF metal and AF metal to AF insulator. We argue that such intermediate phases are possibly related to the puzzling AF metallic state with small magnetization observed in undoped iron-pnictide superconductors as well as to the pseudogap features observed in optical experiments.Comment: 4 pages, 5 figures, accepted in Phys. Rev. B(RC

Orbital selective phase transition induced by different magnetic states: A dynamical cluster approximation study

Motivated by the unexplored complexity of phases present in the multiorbital Hubbard model, we analyze in this work the behavior of a degenerate two-orbital anisotropic Hubbard model at half filling where both orbitals have equal bandwidths and one orbital is constrained to be paramagnetic (PM), while the second one is allowed to have an antiferromagnetic (AF) solution. Such a model may be relevant for a large class of correlated materials with competing magnetic states in different orbitals like the recently discovered Fe-based superconductors. Using a dynamical cluster approximation we observe that novel orbital selective phase transitions appear regardless of the strength of the Ising Hund's rule coupling $J_z$. Moreover, the PM orbital undergoes a transition from a Fermi liquid (FL) to a Mott insulator through a non-FL phase while the AF orbital shows a transition from a FL to an AF insulator through an AF metallic phase. We discuss the implications of the results in the context of the Fe-based superconductors.Comment: 5 pages and 5 figures, and accepted in Rapid communication in PR