Negative Hydration Expansion in ZrW_{2}O_{8}: Microscopic Mechanism, Spaghetti Dynamics, and Negative Thermal Expansion.

We use a combination of x-ray diffraction, total scattering, and quantum mechanical calculations to determine the mechanism responsible for hydration-driven contraction in ZrW_{2}O_{8}. The inclusion of H_{2}O molecules within the ZrW_{2}O_{8} network drives the concerted formation of new W─O bonds to give one-dimensional (─W─O─)_{n} strings. The topology of the ZrW_{2}O_{8} network is such that there is no unique choice for the string trajectories: the same local changes in coordination can propagate with a large number of different periodicities.

Polycatenated 2D Hydrogen-Bonded Binary Supramolecular Organic Frameworks (SOFs) with Enhanced Gas Adsorption and Selectivity.

Controlled assembly of two-dimensional (2D) supramolecular organic frameworks (SOFs) has been demonstrated through a binary strategy in which 1,4-bis-(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)naphthalene (), generated by oxidative dehydrogenation of 1,4-bis-(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)naphthalene (), is coupled in a 1:1 ratio with terphenyl-3,3',4,4'-tetracarboxylic acid (; to form ), 5,5'-(anthracene-9,10-diyl)diisophthalic acid (; to form ), or 5,5'-bis-(azanediyl)-oxalyl-diisophthalic acid (; to form ). Complementary O-H···N hydrogen bonds assemble 2D 6- (honeycomb) subunits that pack as layers in to give a three-dimensional (3D) supramolecular network with parallel channels hosting guest DMF (DMF = ,'-dimethylformamide) molecules. and feature supramolecular networks of 2D → 3D inclined polycatenation of similar layers as those in .

Hidden quasiparticles and incoherent photoemission spectra in Na2IrO3.

We study two Kitaev-Heisenberg t-J-like models on a honeycomb lattice, focusing on the zigzag magnetic phase of Na(2)IrO(3), and investigate hole motion by exact diagonalization and variational methods. The spectral functions are quite distinct from those of cuprates and are dominated by large incoherent spectral weight at high energy, almost independent of the microscopic parameters-a universal and generic feature for zigzag magnetic correlations. We explain why quasiparticles at low energy are strongly suppressed in the photoemission spectra and determine an analog of a pseudogap.

Quantum melting of valence-bond crystal insulators and novel supersolid phase at commensurate density.

Bosonic and fermionic Hubbard models on the checkerboard lattice are studied numerically for infinite on-site repulsion. At particle density n=1/4 and strong nearest-neighbor repulsion, insulating Valence-Bond crystals (VBC) of resonating particle pairs are stabilized. Their melting into superfluid or metallic phases under increasing hopping is investigated at T=0 K.