Phase diagram of a distorted kagome antiferromagnet and application to Y kapellasite

We investigate the magnetism of a previously unexplored distorted spin 1 2 kagome model consisting of three symmetry inequivalent nearest neighbor antiferromagnetic Heisenberg couplings Jhex, J, and J , and uncover a rich ground state phase diagram even at the classical level. Using analytical arguments and numerical techniques we identify a collinear Q 0 magnetic phase, two unusual non collinear coplanar Q 1 3,1 3 phases and a classical spin liquid phase with a degenerate manifold of non coplanar ground states, resembling the jammed spin liquid phase found in the context of a bond disordered kagome antiferromagnet. We further show with density functional theory calculations that the recently synthesized Y kapellasite Y3Cu9 OH 19Cl8 is a realization of this model and predict its ground state to lie in the region of Q 1 3,1 3 order, which remains stable even after the inclusion of quantum fluctuation effects within variational Monte Carlo and pseudofermion functional renormalization group. The presented model opens a new direction in the study of kagome antiferromagnet

Nanoscale Processing by Adaptive Laser Pulses

We theoretically demonstrate that atomically-precise ``nanoscale processing" can be reproducibly performed by adaptive laser pulses. We present the new approach on the controlled welding of crossed carbon nanotubes, giving various metastable junctions of interest. Adaptive laser pulses could be also used in preparation of other hybrid nanostructures.Comment: 4 pages, 4 Postscript figure

Evidence for a three dimensional quantum spin liquid in PbCuTe2O6

The quantum spin liquid is a highly entangled magnetic state characterized by the absence of static magnetism in its ground state. Instead, the spins fluctuate in a highly correlated way down to the lowest temperatures. Quantum spin liquids are very rare and are confined to a few specific cases where the interactions between the magnetic ions cannot be simultaneously satisfied known as frustration . Lattices with magnetic ions in triangular or tetrahedral arrangements, which interact via isotropic antiferromagnetic interactions, can generate such a frustration. Three dimensional isotropic spin liquids have mostly been sought in materials where the magnetic ions form pyrochlore or hyperkagome lattices. Here we present a three dimensional lattice called the hyper hyperkagome that enables spin liquid behaviour and manifests in the compound PbCuTe2O6. Using a combination of experiment and theory, we show that this system exhibits signs of being a quantum spin liquid with no detectable static magnetism together with the presence of diffuse continua in the magnetic spectrum suggestive of fractional spinon excitation

Droplet-like Fermi surfaces in the anti-ferromagnetic phase of EuFe2_2As2_2, an Fe-pnictide superconductor parent compound

Using angle resolved photoemission it is shown that the low lying electronic states of the iron pnictide parent compound EuFe$_2$As$_2$ are strongly modified in the magnetically ordered, low temperature, orthorhombic state compared to the tetragonal, paramagnetic case above the spin density wave transition temperature. Back-folded bands, reflected in the orthorhombic/ anti-ferromagnetic Brillouin zone boundary hybridize strongly with the non-folded states, leading to the opening of energy gaps. As a direct consequence, the large Fermi surfaces of the tetragonal phase fragment, the low temperature Fermi surface being comprised of small droplets, built up of electron and hole-like sections. These high resolution ARPES data are therefore in keeping with quantum oscillation and optical data from other undoped pnictide parent compounds.Comment: 4 figures, 6 page

Zigzag antiferromagnetic quantum ground state in monoclinic honeycomb lattice antimonates A3Ni2SbO6 (A=Li, Na)

We present a comprehensive experimental and theoretical study of the electronic and magnetic properties of two quasi-two-dimensional (2D) honeycomb-lattice monoclinic compounds A3Ni2SbO6 (A=Li, Na). Magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic (AFM) long range order at low temperatures with Néel temperatures ~ 14 and 16 K for Li3Ni2SbO6 and Na3Ni2SbO6, respectively. The effective magnetic moments of 4.3 Bohr magnetons/f.u. (Li3Ni2SbO6) and 4.4 Bohr magnetons/f.u. (Na3Ni2SbO6) indicate that Ni2+ is in a high-spin configuration (S=1). The temperature dependence of the inverse magnetic susceptibility follows the Curie-Weiss law in the high-temperature region and shows positive values of the Weiss temperature ~ 8 K (Li3Ni2SbO6) and ~12 K (Na3Ni2SbO6) pointing to the presence of non-negligible ferromagnetic interactions, although the system orders AFM at low temperatures. In addition, the magnetization curves reveal a field-induced (spin-flop type) transition below TN that can be related to the magnetocrystalline anisotropy in these systems. These observations are in agreement with density functional theory calculations, which show that both antiferromagnetic and ferromagnetic intralayer spin exchange couplings between Ni2+ ions are present in the honeycomb planes supporting a zigzag antiferromagnetic ground state. Based on our experimental measurements and theoretical calculations we propose magnetic phase diagrams for the two compounds