Generalized mean-field study of a driven lattice gas

Generalized mean-field analysis has been performed to study the ordering process in a half-filled square lattice-gas model with repulsive nearest neighbor interaction under the influence of a uniform electric field. We have determined the configuration probabilities on 2-, 4-, 5-, and 6-point clusters excluding the possibility of sublattice ordering. The agreement between the results of 6-point approximations and Monte Carlo simulations confirms the absence of phase transition for sufficiently strong fields.Comment: 4 pages (REVTEX) with 4 PS figures (uuencoded

Dough reological and kernel hardness investigation on different Hungarian winter wheat varieties

The aim of this research was the investigation of winter wheat varieties, the kernel hardness and the dough features. We determined the kernel hardness with two dynamic methods. We measured the parameters of flour. The correlations among hardness index and the examined flour parameters were also significant (r=0.816-0.876). We found strong correlation between the grinding energy (eg) and water absorption (r=0.878) of the flour. Hardness index – wet gluten (r=0.833), and hardness index – water absorption (r=0.876), hardness index – P value of alveograph (r=0.816) showed also positive correlations. We found correlation the water absorption and P value of alveograph (r=0.873)

Main-Belt Asteroids in the K2 Engineering Field of View

Unlike NASA's original Kepler Discovery Mission, the renewed K2 Mission will stare at the plane of the Ecliptic, observing each field for approximately 75 days. This will bring new opportunities and challenges, in particular the presence of a large number of main-belt asteroids that will contaminate the photometry. The large pixel size makes K2 data susceptible to the effect of apparent minor planet encounters. Here we investigate the effects of asteroid encounters on photometric precision using a sub-sample of the K2 Engineering data taken in February, 2014. We show examples of asteroid contamination to facilitate their recognition and distinguish these events from other error sources. We conclude that main-belt asteroids will have considerable effects on K2 photometry of a large number of photometric targets during the Mission, that will have to be taken into account. These results will be readily applicable for future space photometric missions applying large-format CCDs, such as TESS and PLATO.Comment: accepted for publication in AJ, 6 page

Phase transition and selection in a four-species cyclic Lotka-Volterra model

We study a four species ecological system with cyclic dominance whose individuals are distributed on a square lattice. Randomly chosen individuals migrate to one of the neighboring sites if it is empty or invade this site if occupied by their prey. The cyclic dominance maintains the coexistence of all the four species if the concentration of vacant sites is lower than a threshold value. Above the treshold, a symmetry breaking ordering occurs via growing domains containing only two neutral species inside. These two neutral species can protect each other from the external invaders (predators) and extend their common territory. According to our Monte Carlo simulations the observed phase transition is equivalent to those found in spreading models with two equivalent absorbing states although the present model has continuous sets of absorbing states with different portions of the two neutral species. The selection mechanism yielding symmetric phases is related to the domain growth process whith wide boundaries where the four species coexist.Comment: 4 pages, 5 figure

Metals, fractional metals, and superconductivity in rhombohedral trilayer graphene

Combining mean-field and renormalization group analyses, here we unveil the nature of recently observed superconductivity and parent metallic states in chemically doped rhombohedral trilayer graphene, subject to external electric displacement fields (D) [H. Zhou et al., Nature (London) 598, 434 (2021)]. We argue that close to the charge neutrality, on site Hubbard repulsion favors layer antiferromagnet, which when combined with the D-field induced layer polarization, produces a spin-polarized, but valley-unpolarized half metal, conducive to the nucleation of spin-triplet f-wave pairing (SC2). At larger doping valence bond order emerges as a prominent candidate for isospin coherent paramagent, boosting condensation of spin-singlet Cooper pairs in the s-wave channel (SC1), manifesting a "selection rule" among competing orders. Responses of these paired states to displacement and in-plane magnetic fields show qualitative similarities with experimental observation. With the onset of the quantum anomalous Hall order, the valley degeneracy of half metal gets lifted, forming a quarter metal at lower doping [H. Zhou et al., Nature (London) 598, 429 (2021)]

Competing orders and cascade of degeneracy lifting in doped Bernal bilayer graphene

Motivated by recent experiments [H. Zhou et al., Science 375, 774 (2022) and S. C. de la Barrera et al., arXiv:2110.13907], here we propose a general mechanism for valley and/or spin degeneracy lifting of the electronic bands in doped Bernal bilayer graphene, subject to electric displacement (D) fields. A D-field induced layer polarization (LP), when accompanied by a Hubbard repulsion-driven layer antiferromagnet (LAF) and next-nearest-neighbor repulsion-driven quantum anomalous Hall (QAH) orders, lifts the fourfold degeneracy of electronic bands, yielding a quarter metal for small doping, as also observed in ABC trilayer graphene. With the disappearance of the QAH order, electronic bands recover twofold valley degeneracy, thereby forming a conventional or compensated (with majority and minority carriers) half metal at moderate doping, depending on the relative strength of LP and LAF. At even higher doping and for a weak D field only LAF survives and the Fermi surface recovers fourfold degeneracy. We also show that a pure repulsive electronic interaction mediated triplet f -wave pairing emerges from a parent correlated nematic liquid or compensated half metal when an in-plane magnetic field is applied to the system

Extended Hubbard model in undoped and doped monolayer and bilayer graphene: Selection rules and organizing principle among competing orders

Performing a leading-order renormalization group analysis, here we compute the effects of generic local or short-range electronic interactions in monolayer and the Bernal bilayer graphene. Respectively in these two systems, gapless chiral quasiparticles display linear and biquadratic band touching, leading to linearly vanishing and constant density of states. Consequently, the former system remains stable for weak enough local interactions and supports a variety of ordered phases only beyond a critical strength of interactions. By contrast, ordered phases can nucleate for sufficiently weak interactions in bilayer graphene. By tuning the strength of all symmetry allowed local interactions, we construct various cuts of the phase diagram at zero and finite temperature and chemical doping. Typically, at zero doping, insulating phases (such as charge density wave, antiferromagnet, quantum anomalous, and spin Hall insulators) prevail at the lowest temperature, while gapless nematic or smectic liquids stabilize at higher temperatures. On the other hand, at finite doping, the lowest temperature ordered phase is occupied by a superconductor. Besides anchoring such an organizing principle among the candidate ordered phases, we also establish a selection rule between them and the interaction channel responsible for the breakdown of linear or biquadratic chiral nodal Fermi liquid. In addition, we also demonstrate the role of the normal state band structure in selecting the pattern of symmetry breaking from a soup of preselected incipient competing orders. As a direct consequence of the selection rule, while an antiferromagnetic phase develops in undoped monolayer and bilayer graphene, the linear (biquadratic) band dispersion favors condensation of a spin-singlet nematic (translational symmetry breaking Kekule) superconductor in doped monolayer (bilayer) graphene, when the on-site Hubbard repulsion dominates in these systems. On the other hand, nearest-neighbor (next-nearest-neighbor) repulsion accommodates charge density wave (quantum spin Hall insulator) and s + i f (s-wave) pairing at zero and finite chemical doping in both systems, respectively