Quantifying nonuniversal corner free-energy contributions in weakly anisotropic two-dimensional critical systems.

We derive an exact formula for the corner free-energy contribution of weakly anisotropic two-dimensional critical systems in the Ising universality class on rectangular domains, expressed in terms of quantities that specify the anisotropic fluctuations. The resulting expression agrees with numerical exact calculations that we perform for the anisotropic triangular Ising model and quantifies the nonuniversality of the corner term for anisotropic critical two-dimensional systems. Our generic formula is expected to apply also to other weakly-anisotropic critical two-dimensional systems that allow for a conformal field theory description in the isotropic limit.

Sublattice-selective percolation on bipartite planar lattices.

In conventional site percolation, all lattice sites are occupied with the same probability. For a bipartite lattice, sublattice-selective percolation instead involves two independent occupation probabilities, depending on the sublattice to which a given site belongs. Here, we determine the corresponding phase diagram for the two-dimensional square and Lieb lattices from quantifying the parameter regime where a percolating cluster persists for sublattice-selective percolation.

Reduced basis surrogates for quantum spin systems based on tensor networks.

Within the reduced basis methods approach, an effective low-dimensional subspace of a quantum many-body Hilbert space is constructed in order to investigate, e.g., the ground-state phase diagram.

Haldane topological spin-1 chains in a planar metal-organic framework.

Haldane topological materials contain unique antiferromagnetic chains with symmetry-protected energy gaps. Such materials have potential applications in spintronics and future quantum computers. Haldane topological solids typically consist of spin-1 chains embedded in extended three-dimensional (3D) crystal structures.

Evidence for pressure induced unconventional quantum criticality in the coupled spin ladder antiferromagnet CHNCuBr.

Quantum phase transitions in quantum matter occur at zero temperature between distinct ground states by tuning a nonthermal control parameter. Often, they can be accurately described within the Landau theory of phase transitions, similarly to conventional thermal phase transitions. However, this picture can break down under certain circumstances.

Surrogate models for quantum spin systems based on reduced-order modeling.

We present a methodology to investigate phase diagrams of quantum models based on the principle of the reduced basis method (RBM). The RBM is built from a few ground-state snapshots, i.e.

Exact Critical Casimir Amplitude of Anisotropic Systems from Conformal Field Theory and Self-Similarity of Finite-Size Scaling Functions in d≥2 Dimensions.

The exact critical Casimir amplitude is derived for anisotropic systems within the d=2 Ising universality class by combining conformal field theory with anisotropic φ^{4} theory. Explicit results are presented for the general anisotropic scalar φ^{4} model and for the fully anisotropic triangular-lattice Ising model in finite rectangular and infinite strip geometries with periodic boundary conditions. These results demonstrate the validity of multiparameter universality for confined anisotropic systems and the nonuniversality of the critical Casimir amplitude.

Preparation and Evaluation of Antimicrobial Hyperbranched Emulsifiers for Waterborne Coatings.

Nosocomial infections are a major problem in medical health care. To solve this problem, a series of antimicrobial waterborne paints were prepared by using antimicrobial hyperbranched (HB) emulsifiers. The HB-emulsifiers were prepared by polymerizing AB monomers obtained in a one-step reaction of bis(hexamethylene)triamine and carbonyl biscaprolactam.

Diagnosing Fractionalization from the Spin Dynamics of Z_{2} Spin Liquids on the Kagome Lattice by Quantum Monte Carlo Simulations.

Based on large-scale quantum Monte Carlo simulations, we examine the dynamical spin structure factor of the Balents-Fisher-Girvin kagome lattice spin-1/2 model, which is known to harbor an extended Z_{2} quantum spin liquid phase. We use a correlation-matrix sampling scheme combined with a stochastic analytic continuation method to resolve the spectral functions of this anisotropic quantum spin model with a three-site unit cell. Based on this approach, we monitor the spin dynamics throughout the phase diagram of this model, from the XY-ferromagnetic region to the Z_{2} quantum spin liquid regime.

Transmission of Monospecies and Dual-Species Biofilms from Smooth to Nanopillared Surfaces.

The transmission of bacteria in biofilms from donor to receiver surfaces precedes the formation of biofilms in many applications. Biofilm transmission is different from bacterial adhesion, because it involves biofilm compression in between two surfaces, followed by a separation force leading to the detachment of the biofilm from the donor surface and subsequent adhesion to the receiver surface. Therewith, the transmission depends on a balance between donor and receiver surface properties and the cohesiveness of the biofilm itself.

Self-perceived mouthfeel and physico-chemical surface effects after chewing gums containing sorbitol and Magnolia bark extract.

The European Food Safety Authority recognizes the contribution of sugar-free chewing gum to oral health through increased salivation, clearance of food debris, and neutralization of biofilm pH. Magnolia bark extract is a gum additive shown to reduce the prevalence of bad-breath bacteria but its effects on self-perceived mouthfeel are unknown. This paper aims to relate the effects of sorbitol-containing chewing gum, with and without Magnolia bark extract, on tooth-surface hydrophobicity and salivary-film composition with self-perceived mouthfeel.

Potential benefits of chewing gum for the delivery of oral therapeutics and its possible role in oral healthcare.

Introduction: Over the years, chewing gum has developed from a candy towards an oral health-promoting nutraceutical. This review summarizes evidence for the oral health benefits of chewing gum, emphasizing identification of active ingredients in gum that facilitate prevention and removal of oral biofilm.

Areas Covered: Chewing of sugar-free gum yields oral health benefits that include clearance of food debris, reduction in oral dryness, increase of biofilm pH and remineralization of enamel.

Quantification and qualification of bacteria trapped in chewed gum.

Chewing of gum contributes to the maintenance of oral health. Many oral diseases, including caries and periodontal disease, are caused by bacteria. However, it is unknown whether chewing of gum can remove bacteria from the oral cavity.

Quantum nature of edge magnetism in graphene.

It is argued that the subtle crossover from decoherence-dominated classical magnetism to fluctuation-dominated quantum magnetism is experimentally accessible in graphene nanoribbons. We show that the width of a nanoribbon determines whether the edge magnetism is on the classical side, on the quantum side, or in between. In the classical regime, decoherence is dominant and leads to static spin polarizations at the ribbon edges, which are well described by mean-field theories.

Thermal phase transitions in a honeycomb lattice gas with three-body interactions.

We study the thermal phase transitions in a classical (hard-core) lattice gas model with nearest-neighbor three-body interactions on the honeycomb lattice, based on parallel tempering Monte Carlo simulations. This system realizes incompressible low-temperature phases at fractional fillings of 9/16, 5/8, and 3/4 that were identified in a previous study of a related quantum model. In particular, both the 9/16 and the 5/8 phase exhibit an extensive ground-state degeneracy reflecting the frustrated nature of the three-body interactions on the honeycomb lattice.

Magnetic correlations in short and narrow graphene armchair nanoribbons.

Electronic states at the ends of a narrow armchair nanoribbon give rise to a pair of nonlocally entangled spins. We propose two experiments to probe these magnetic states, based on magnetometry and tunneling spectroscopy, in which correlation effects lead to a striking, nonlinear response to external magnetic fields. On the basis of low-energy theories that we derive here, it is remarkably simple to assess these nonlinear signatures for magnetic edge states.

Dimerized solids and resonating plaquette order in SU(N)-Dirac fermions.

We study the quantum phases of fermions with an explicit SU(N)-symmetric, Heisenberg-like nearest-neighbor flavor exchange interaction on the honeycomb lattice at half filling. Employing projective (zero temperature) quantum Monte Carlo simulations for even values of N, we explore the evolution from a weak-coupling semimetal into the strong-coupling, insulating regime. Furthermore, we compare our numerical results to a saddle-point approximation in the large-N limit.

Stiffness jump in the generalized XY model on the square lattice.

We study the thermal phase transitions in the generalized classical XY model on the two-dimensional square lattice using single-cluster Monte Carlo simulations. In particular, we examine the (spin-wave) stiffness (helicity modulus) jump at the transition between the low-temperature algebraic phases and the disordered high-temperature regime. Employing a finite-size scaling ansatz from conformal field theory to estimate the termination of the algebraic phases that does not require knowledge of the critical properties, we provide an unbiased estimate of the stiffness jump.

Adiabatic loading of one-dimensional SU(N) alkaline-earth-atom fermions in optical lattices.

Ultracold fermionic alkaline earth atoms confined in optical lattices realize Hubbard models with internal SU(N) symmetries, where N can be as large as ten. Such systems are expected to harbor exotic magnetic physics at temperatures below the superexchange energy scale. Employing quantum Monte Carlo simulations to access the low-temperature regime of one-dimensional chains, we show that after adiabatically loading a weakly interacting gas into the strongly interacting regime of an optical lattice, the final temperature decreases with increasing N.

Antiferromagnetism in the Hubbard model on the Bernal-stacked honeycomb bilayer.

Using a combination of quantum Monte Carlo simulations, functional renormalization group calculations and mean-field theory, we study the Hubbard model on the Bernal-stacked honeycomb bilayer at half-filling as a model system for bilayer graphene. The free bands consisting of two Fermi points with quadratic dispersions lead to a finite density of states at the Fermi level, which triggers an antiferromagnetic instability that spontaneously breaks sublattice and spin rotational symmetry once local Coulomb repulsions are introduced. Our results reveal an inhomogeneous participation of the spin moments in the ordered ground state, with enhanced moments at the threefold coordinated sites.

Dynamical signatures of edge-state magnetism on graphene nanoribbons.

We investigate the edge-state magnetism of graphene nanoribbons using projective quantum Monte Carlo simulations and a self-consistent mean-field approximation of the Hubbard model. The static magnetic correlations are found to be short ranged. Nevertheless, the correlation length increases with the width of the ribbon such that already for ribbons of moderate widths we observe a strong trend towards mean-field-type ferromagnetic correlations at a zigzag edge.

Pair superfluidity of three-body constrained bosons in two dimensions.

We examine the equilibrium properties of lattice bosons with attractive on-site interactions in the presence of a three-body hard-core constraint that stabilizes the system against collapse and gives rise to a dimer superfluid phase. Employing quantum Monte Carlo simulations, the ground state phase diagram of this system on the square lattice is analyzed. In particular, we study the quantum phase transition between the atomic and dimer superfluid regime and analyze the nature of the superfluid-insulator transitions.

Bose-glass phases in disordered quantum magnets.

In disordered spin systems with antiferromagnetic Heisenberg exchange, transitions into and out of a magnetic-field-induced ordered phase pass through unique regimes. Using quantum Monte Carlo simulations to study the zero-temperature behavior, these intermediate regions are determined to be Bose-glass phases. The localization of field-induced triplons causes a finite compressibility and, hence, glassiness in the disordered phase.

Supersolid hard-core bosons on the triangular lattice.

We determine the phase diagram of hard-core bosons on a triangular lattice with nearest-neighbor repulsion, paying special attention to the stability of the supersolid phase. Similar to the same model on a square lattice we find that for densities rho<1/3 or rho>2/3 a supersolid phase is unstable and the transition between a commensurate solid and the superfluid is of first order. At intermediate fillings 1/3 View Article and Find Full Text PDF

Generalized directed loop method for quantum Monte Carlo simulations.

Efficient quantum Monte Carlo update schemes called directed loops have recently been proposed, which improve the efficiency of simulations of quantum lattice models. We propose to generalize the detailed balance equations at the local level during the loop construction by accounting for the matrix elements of the operators associated with open world-line segments. Using linear programming techniques to solve the generalized equations, we look for optimal construction schemes for directed loops.