33 research outputs found
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 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 . 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