@article{MinGothLutzetal.2017,
  author    = {Min, Chul-Hee and Goth, F. and Lutz, P. and Bentmann, H. and Kang, B.Y. and Cho, B.K. and Werner, J. and Chen, K.-S. and Assaad, F. and Reinert, F.},
  title     = {Matching DMFT calculations with photoemission spectra of heavy fermion insulators: universal properties of the near-gap spectra of SmB\(_{6}\)},
  series = {Scientific Reports},
  volume    = {7},
  journal   = {Scientific Reports},
  number    = {11980},
  doi       = {10.1038/s41598-017-12080-5},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170328},
  year      = {2017},
  abstract  = {Paramagnetic heavy fermion insulators consist of fully occupied quasiparticle bands inherent to Fermi liquid theory. The gap emergence below a characteristic temperature is the ultimate sign of coherence for a many-body system, which in addition can induce a non-trivial band topology. Here, we demonstrate a simple and efficient method to compare a model study and an experimental result for heavy fermion insulators. The temperature dependence of the gap formation in both local moment and mixed valence regimes is captured within the dynamical mean field (DMFT) approximation to the periodic Anderson model (PAM). Using the topological coherence temperature as the scaling factor and choosing the input parameter set within the mixed valence regime, we can unambiguously link the theoretical energy scales to the experimental ones. As a particularly important result, we find improved consistency between the scaled DMFT density of states and the photoemission near-gap spectra of samarium hexaboride (SmB\(_{6}\)).},
  language  = {en}
}
@article{AssaadHerbut2013,
  author    = {Assaad, Fakher F. and Herbut, Igor F.},
  title     = {Pinning the Order: The Nature of Quantum Criticality in the Hubbard Model on Honeycomb Lattice},
  series = {Physical Review X},
  volume    = {3},
  journal   = {Physical Review X},
  number    = {031010},
  doi       = {10.1103/PhysRevX.3.031010},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-129829},
  year      = {2013},
  abstract  = {In numerical simulations, spontaneously broken symmetry is often detected by computing two-point correlation functions of the appropriate local order parameter. This approach, however, computes the square of the local order parameter, and so when it is small, very large system sizes at high precisions are required to obtain reliable results. Alternatively, one can pin the order by introducing a local symmetrybreaking field and then measure the induced local order parameter infinitely far from the pinning center. The method is tested here at length for the Hubbard model on honeycomb lattice, within the realm of the projective auxiliary-field quantum Monte Carlo algorithm. With our enhanced resolution, we find a direct and continuous quantum phase transition between the semimetallic and the insulating antiferromagnetic states with increase of the interaction. The single-particle gap, measured in units of Hubbard U, tracks the staggered magnetization. An excellent data collapse is obtained by finite-size scaling, with the values of the critical exponents in accord with the Gross-Neveu universality class of the transition.},
  language  = {en}
}
@article{AssaadBercxHohenadler2013,
  author    = {Assaad, F. F. and Bercx, M. and Hohenadler, M.},
  title     = {Topological Invariant and Quantum Spin Models from Magnetic pi Fluxes in Correlated Topological Insulators},
  series = {Physical Review X},
  volume    = {3},
  journal   = {Physical Review X},
  number    = {1},
  doi       = {10.1103/PhysRevX.3.011015},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-129849},
  year      = {2013},
  abstract  = {The adiabatic insertion of a \(\pi\) flux into a quantum spin Hall insulator gives rise to localized spin and charge fluxon states. We demonstrate that \(\pi\) fluxes can be used in exact quantum Monte Carlo simulations to identify a correlated \(Z_2\) topological insulator using the example of the Kane-Mele-Hubbard model. In the presence of repulsive interactions, a \(\pi\) flux gives rise to a Kramers doublet of spin-fluxon states with a Curie-law signature in the magnetic susceptibility. Electronic correlations also provide a bosonic mode of magnetic excitons with tunable energy that act as exchange particles and mediate a dynamical interaction of adjustable range and strength between spin fluxons. \(\pi\) fluxes can therefore be used to build models of interacting spins. This idea is applied to a three-spin ring and to one-dimensional spin chains. Because of the freedom to create almost arbitrary spin lattices, correlated topological insulators with \(\pi\) fluxes represent a novel kind of quantum simulator, potentially useful for numerical simulations and experiments.},
  language  = {en}
}
@article{RoyAssaadHerbut2014,
  author    = {Roy, Bitan and Assaad, Fakher F. and Herbut, Igor F.},
  title     = {Zero Modes and Global Antiferromagnetism in Strained Graphene},
  series = {Physical Review X},
  volume    = {4},
  journal   = {Physical Review X},
  number    = {2},
  issn      = {2160-3308},
  doi       = {10.1103/PhysRevX.4.021042},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-116108},
  pages     = {21042},
  year      = {2014},
  abstract  = {A novel magnetic ground state is reported for the Hubbard Hamiltonian in strained graphene. When the chemical potential lies close to the Dirac point, the ground state exhibits locally both the Neel and ferromagnetic orders, even for weak Hubbard interaction. Whereas the Neel order parameter remains of the same sign in the entire system, the magnetization at the boundary takes the opposite sign from the bulk. The total magnetization vanishes this way, and the magnetic ground state is globally only an antiferromagnet. This peculiar ordering stems from the nature of the strain-induced single-particle zero-energy states, which have support on one sublattice of the honeycomb lattice in the bulk, and on the other sublattice near the boundary of a finite system. We support our claim with the self-consistent numerical calculation of the order parameters, as well as by the Monte Carlo simulations of the Hubbard model in both uniformly and nonuniformly strained honeycomb lattice. The present result is contrasted with the magnetic ground state of the same Hubbard model in the presence of a true magnetic field (and for vanishing Zeeman coupling), which is exclusively Neel ordered, with zero local magnetization everywhere in the system.},
  language  = {en}
}