810 research outputs found
Efficient calculation of imaginary time displaced correlation functions in the projector auxiliary field quantum Monte-Carlo algorithm
The calculation of imaginary time displaced correlation functions with the
auxiliary field projector quantum Monte-Carlo algorithm provides valuable
insight (such as spin and charge gaps) in the model under consideration. One of
the authors and M. Imada [F.F. Assaad and M. Imada, J. Phys. Soc. Jpn. 65 189
(1996).] have proposed a numerically stable method to compute those quantities.
Although precise this method is expensive in CPU time. Here, we present an
alternative approach which is an order of magnitude quicker, just as precise,
and very simple to implement. The method is based on the observation that for a
given auxiliary field the equal time Green function matrix, , is a
projector: .Comment: 4 papes, 1 figure in eps forma
Metamagnetism and Lifshitz Transitions in Models for Heavy Fermions
We investigate metamagnetic transitions in models for heavy fermions by
considering the doped Kondo lattice model in two dimensions. Results are
obtained within the framework of dynamical mean field and dynamical cluster
approximations. Universal magnetization curves for different temperatures and
Kondo couplings develop upon scaling with the lattice coherence temperature.
Furthermore, the coupling of the local moments to the magnetic field is varied
to take into account the different Land\'e factors of localized and itinerant
electrons. The competition between the lattice coherence scale and the Zeeman
energy scale allows for two interpretations of the metamagnetism in heavy
fermions: Kondo breakdown or Lifshitz transitions. By tracking the
single-particle residue through the transition, we can uniquely conclude in
favor of the Lifshitz transition scenario. In this scenario, a quasiparticle
band drops below the Fermi energy which leads to a change in topology of the
Fermi surface.Comment: 8 pages, 7 figure
Reply to a Comment on ``Projective Quantum Monte Carlo Method for the Anderson Impurity Model and its Application to Dynamical Mean Field Theory''
In our reply, we show that the objections put forward in cond-mat/0508763
concerning our paper, Phys. Rev. Lett. 93, 136405 (2004), are not valid:
(i) There is no orthogonality catastrophe (OC) for our calculations, and it
is also generally not ``unpractical'' to avoid it.
(ii) The OC does not affect our results.Comment: 1 page, 1 figure, Phys. Rev. Lett. in print; also note
cond-mat/050944
Luttinger Liquid Physics and Spin-Flip Scattering on Helical Edges
We investigate electronic correlation effects on edge states of quantum
spin-Hall insulators within the Kane-Mele-Hubbard model by means of quantum
Monte Carlo simulations. Given the U(1) spin symmetry and time-reversal
invariance, the low-energy theory is the helical Tomanaga-Luttinger model, with
forward scattering only. For weak to intermediate interactions, this model
correctly describes equal-time spin and charge correlations, including their
doping dependence. As apparent from the Drude weight, bulk states become
relevant in the presence of electron-electron interactions, rendering the
forward-scattering model incomplete. Strong correlations give rise to slowly
decaying transverse spin fluctuations, and inelastic spin-flip scattering
strongly modifies the single-particle spectrum, leading to graphene-like edge
state signatures. The helical Tomanaga-Luttinger model is completely valid only
asymptotically in the weak-coupling limit.Comment: 5 pages, 5 figures (modified version with additional data
Doping induced metal-insulator transition in two-dimensional Hubbard, , and extended Hubbard, , models
We show numerically that the nature of the doping induced metal-insulator
transition in the two-dimensional Hubbard model is radically altered by the
inclusion of a term, , which depends upon a square of a single-particle
nearest-neighbor hopping. This result is reached by computing the localization
length, , in the insulating state. At finite values of we find
results consistent with where is
the critical chemical potential. In contrast, for the Hubbard model. At finite values of , the presented
numerical results imply that doping the antiferromagnetic Mott insulator leads
to a superconductor.Comment: 19 pages (latex) including 7 figures in encapsulated postscript
format. Submitted for publication in Phys. Rev.
- …