Spinon Fermi surface in a cluster Mott insulator model on a triangular lattice and possible application to 1T-TaS2_2

1T-TaS$_2$ is a cluster Mott insulator on the triangular lattice with 13 Ta atoms forming a star of David cluster as the unit cell. We derive a two dimensional XXZ spin-1/2 model with four-spin ring exchange term to describe the effective low energy physics of a monolayer 1T-TaS$_2$, where the effective spin-1/2 degrees of freedom arises from the Kramers degenerate spin-orbital states on each star of David. A large scale density matrix renormalization group simulation is further performed on this effective model and we find a gapless spin liquid phase with spinon Fermi surface at moderate to large strength region of four-spin ring exchange term. All peaks in the static spin structure factor are found to be located on the "$2k_F$" surface of half-filled spinon on the triangular lattice. Experiments to detect the spinon Fermi surface phase in 1T-TaS$_2$ are discussed.Comment: 5+11 pages, 4+13 figure

(Z)-1-[4-Fluoro-2-(pyrrolidin-1-yl)phen­yl]-3-phenyl-2-(1H-1,2,4-triazol-1-yl)prop-2-en-1-one

In the title mol­ecule, C21H19FN4O, the triazole ring forms dihedral angles of 67.0 (1) and 59.6 (1)° with the phenyl and fluoro-substituted benzene rings, respectively. The dihedral angle between the phenyl ring and the fluoro-substituted benzene ring is 79.1 (1)°. The pyrrolidine ring is in a half-chair conformation. In the crystal, weak C—H⋯O and C—H⋯N hydrogen bonds connect mol­ecules into layers parallel to (001)

Strain Induced One-Dimensional Landau-Level Quantization in Corrugated Graphene

Theoretical research has predicted that ripples of graphene generates effective gauge field on its low energy electronic structure and could lead to zero-energy flat bands, which are the analog of Landau levels in real magnetic fields. Here we demonstrate, using a combination of scanning tunneling microscopy and tight-binding approximation, that the zero-energy Landau levels with vanishing Fermi velocities will form when the effective pseudomagnetic flux per ripple is larger than the flux quantum. Our analysis indicates that the effective gauge field of the ripples results in zero-energy flat bands in one direction but not in another. The Fermi velocities in the perpendicular direction of the ripples are not renormalized at all. The condition to generate the ripples is also discussed according to classical thin-film elasticity theory.Comment: 4 figures, Phys. Rev.

Poly[[aqua­bis(μ3-isonicotinato-κ3 O:O′:N)tris­(μ2-isonicotinato-κ3 O,O′:N)(nitrato-κO)bis­(μ4-oxalato-κ6 O 1,O 2:O 2:O 1′,O 2′:O 1′)dierbium(III)tetra­silver(I)] tetra­hydrate]

In the title coordination polymer, {[Ag4Er2(C6H4NO2)5(C2O4)2(NO3)(H2O)]·4H2O}n, each ErIII atom is coordinated in a bicapped trigonal–prismatic coordination geometry by three O atoms from two isonicotinate (IN) ligands, four O atoms from two oxalate ligands and one O atom from either a nitrate ion or a water mol­ecule, both of which are half-occupied over the same site. One AgI atom has a Y-shaped geometry defined by one N atom from one IN ligand, one O atom from another IN ligand and one O atom from an oxalate ligand. The other AgI atom is coordinated by two IN ligands and one O atom from an oxalate ligand. One of the IN ligands is disordered over an inversion center and forms a bridge between two centrosymmetric AgI ions. Due to the disorder, this IN ligand coordinates to the Ag atom through either the pyridyl N or the carboxyl­ate O atoms. The IN and oxalate ligands link the Er and Ag atoms into a three-dimensional coordination framework. O—H⋯O and C—H⋯O hydrogen bonds are observed in the crystal structure

The Dynamics of Bimodular Continuous Attractor Neural Networks with Static and Moving Stimuli

The brain achieves multisensory integration by combining the information received from different sensory inputs to yield inferences with higher speed or more accuracy. We consider a bimodular neural network each processing a modality of sensory input and interacting with each other. The dynamics of excitatory and inhibitory couplings between the two modules are studied with static and moving stimuli. The modules exhibit non-trivial interactive behaviors depending on the input strengths, their disparity and speed (for moving inputs), and the inter-modular couplings. They give rise to a family of models applicable to causal inference problems in neuroscience. They also provide a model for the experiment of motion-bounce illusion, yielding consistent results and predicting their robustness.Comment: 15 pages, 12 figures, journal pape