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@PHDTHESIS{Sushchyev:987978,
author = {Sushchyev, Alexander},
othercontributors = {Weßel, Stefan and Kennes, Dante Marvin},
title = {{Q}uantum {M}onte {C}arlo studies of strongly correlated
fermion- and spin-systems with competing interactions},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2024-05967},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2024},
abstract = {In this thesis we study (quantum) phase transitions in
fermion and spin systems. In the first part we consider the
Hubbard model on the square lattice at half filling. For a
more realistic description of real materials with partially
screened Coulomb interactions, we include non-local
repulsive terms. In detail, we include (i) nearest-neighbor
interactions and (ii) long-range Coulomb (LRC) interactions.
Based on DQMC simulations within sign-problem free coupling
regimes we report results for the temperature resolved
double occupancy and entropy, assess a recent study in terms
of a first-order metal-to-insulator transition and discuss
various phase transitions in the vicinity of the analyzed
parameter regime. Continuing DQMC simulations, we examine
the Hubbard model on an ABCA stacked tetra-layer graphene
structure regarding its magnetic ground state properties
over a wide range of the local Hubbard-U. Motivated by
experimental findings, we added an extended layer-to-layer
interaction and analyzed the extended model in the
sign-problem free regime. The second part considers the
Heisenberg model regarding different spinexchange
interactions, based on SSE simulations. We examine the most
generic case of three varying couplings along the
unequivalent directions on a honeycomb lattice, where we
find anomalous finite-size scaling corrections in the Binder
ratio along the quantum phase transition lines between an
AFM order and dimerized unordered states. Finally, we extend
our Heisenberg model studies to the three-dimensional
diamond lattice for both antiferromagnetic as well as
ferromagnetic couplings. We determine the finite critical
temperatures and find the value of the Néel temperature to
be higher than the value for the Curie temperature. We
discuss the stability of the ordered phases against thermal
fluctuations with respect to the low-temperature entropy
gain.},
cin = {135620 / 130000},
ddc = {530},
cid = {$I:(DE-82)135620_20140620$ / $I:(DE-82)130000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2024-05967},
url = {https://publications.rwth-aachen.de/record/987978},
}
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