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

Standard model plethystics

We study the vacuum geometry prescribed by the gauge invariant operators of the minimal supersymmetric standard model via the plethystic program. This is achieved by using several tricks to perform the highly computationally challenging Molien-Weyl integral, from which we extract the Hilbert series, encoding the invariants of the geometry at all degrees. The fully refined Hilbert series is presented as the explicit sum of 1422 rational functions. We found a good choice of weights to unrefine the Hilbert series into a rational function of a single variable, from which we can read off the dimension and the degree of the vacuum moduli space of the minimal supersymmetric standard model gauge invariants. All data in Mathematica format are also presented

Kekul\'e valence bond order in an extended Hubbard model on the honeycomb lattice, with possible applications to twisted bilayer graphene

Using large-scale quantum Monte Carlo simulations, we exactly solve a model of Fermions hopping on the honeycomb lattice with cluster charge interactions, which has been proposed as an effective model with possible application to twisted bilayer graphene near half-filling. We find an interaction driven semimetal to insulator transition to an insulating phase consisting of a valence bond solid with Kekul\'e pattern. Finite size scaling reveals that the phase transition of the semimetal to Kekul\'e valence bond solid phase is continuous and belongs to chiral XY universality class.Comment: 4+1 pages, 4 figure

Thick film magnetic nanoparticulate composites and method of manufacture thereof

Thick film magnetic/insulating nanocomposite materials, with significantly reduced core loss, and their manufacture are described. The insulator coated magnetic nanocomposite comprises one or more magnetic components, and an insulating component. The magnetic component comprises nanometer scale particles (about 1 to about 100 nanometers) coated by a thin-layered insulating phase. While the intergrain interaction between the immediate neighboring magnetic nanoparticles separated by the insulating phase provides the desired soft magnetic properties, the insulating material provides high resistivity, which reduces eddy current loss

Magnetic and structural transitions in La0.4_{0.4}Na0.6_{0.6}Fe2_2As2_2 single crystals

La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals have been grown out of an NaAs flux in an alumina crucible and characterized by measuring magnetic susceptibility, electrical resistivity, specific heat, as well as single crystal x-ray and neutron diffraction. La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals show a structural phase transition from a high temperature tetragonal phase to a low-temperature orthorhombic phase at T$_s$\,=\,125\,K. This structural transition is accompanied by an anomaly in the temperature dependence of electrical resistivity, anisotropic magnetic susceptibility, and specific heat. Concomitant with the structural phase transition, the Fe moments order along the \emph{a} direction with an ordered moment of 0.7(1)\,$\mu_{\textup{B}}$ at \emph{T}\,=\,5 K. The low temperature stripe antiferromagnetic structure is the same as that in other \emph{A}Fe$_{2}$As$_{2}$ (\emph{A}\,=\,Ca, Sr, Ba) compounds. La$_{0.5-x}$Na$_{0.5+x}$Fe$_2$As$_2$ provides a new material platform for the study of iron-based superconductors where the electron-hole asymmetry could be studied by simply varying La/Na ratio.Comment: 9 pages, 7 figures, to appear in Physical Review

Variation of the Fine-Structure Constant from the de Sitter Invariant Special Relativity

There are obvious discrepancies among various experimental constraints on the variation of the fine-structure constant, $\alpha$. We attempt to discuss the issue in the framework of de Sitter invariant Special Relativity (${\cal SR}_{c,R}$) and to present a possible solution to the disagreement. In addition, on the basis of the observational data and the discussions presented in this Letter, we derive a rough theoretical estimate of the radius of the Universe.Comment: 8 pages, no figure

The Vortical Structures in the Rear Separation and Wake Produced by a Supersonic Micro-Ramp

The vortical structures in the rear separation and wake region produced by a micro-ramp that immersed in a supersonic turbulent boundary layer are investigated. The small scale separation close to the trailing edge was reveled and this confirms the previous experimental observation. Between the reverse region and surrounding fast moving flow, a three-dimensional shear layer was formed, and vortices are generated. By using vortex line method, the spiral points were understood as the cross-sections of the Ω-shaped vortices that follow the shape of the separation. The vortical structure was analogous to that in the wake region, where similar Ω-shaped vortex can be observed which follows the deficit region caused by the micro-ramp. Finally, the revealed flow topology was conceived beneficial to studying the wall bounded turbulence which involves similar vortical structures but in a smaller scale, while the vortical pattern in the current micro-ramp wake is larger