36,687 research outputs found
Evidence of spin liquid with hard-core bosons in a square lattice
We show that laser assisted hopping of hard core bosons in a square optical
lattice can be described by an antiferromagnetic - XY model with
tunable ratio of . We numerically investigate the phase diagram of
the - XY model using both the tensor network algorithm for
infinite systems and the exact diagonalization for small clusters and find
strong evidence that in the intermediate region around ,
there is a spin liquid phase with vanishing magnetization and valence bond
orders, which interconnects the Neel state on the side and the
stripe antiferromagnetic phase on the side. This finding
opens up the possibility of studying the exotic spin liquid phase in a
realistic experimental system using ultracold atoms in an optical lattice.Comment: 5 pages, 5 figure
Supersolid and charge density-wave states from anisotropic interaction in an optical lattice
We show anisotropy of the dipole interaction between magnetic atoms or polar
molecules can stabilize new quantum phases in an optical lattice. Using a well
controlled numerical method based on the tensor network algorithm, we calculate
phase diagram of the resultant effective Hamiltonian in a two-dimensional
square lattice - an anisotropic Hubbard model of hard-core bosons with
attractive interaction in one direction and repulsive interaction in the other
direction. Besides the conventional superfluid and the Mott insulator states,
we find the striped and the checkerboard charge density wave states and the
supersolid phase that interconnect the superfluid and the striped solid states.
The transition to the supersolid phase has a mechanism different from the case
of the soft-core Bose Hubbard model.Comment: 5 pages, 5 figures
Topological Bose-Mott Insulators in a One-Dimensional Optical Superlattice
We study topological properties of the Bose-Hubbard model with repulsive
interactions in a one-dimensional optical superlattice. We find that the Mott
insulator states of the single-component (two-component) Bose-Hubbard model
under fractional fillings are topological insulators characterized by a nonzero
charge (or spin) Chern number with nontrivial edge states. For ultracold atomic
experiments, we show that the topological Chern number can be detected through
measuring the density profiles of the bosonic atoms in a harmonic trap.Comment: 5 pages, published versio
Stabilization of the p-wave superfluid state in an optical lattice
It is hard to stabilize the p-wave superfluid state of cold atomic gas in
free space due to inelastic collisional losses. We consider the p-wave Feshbach
resonance in an optical lattice, and show that it is possible to have a stable
p-wave superfluid state where the multi-atom collisional loss is suppressed
through the quantum Zeno effect. We derive the effective Hamiltonian for this
system, and calculate its phase diagram in a one-dimensional optical lattice.
The results show rich phase transitions between the p-wave superfluid state and
different types of insulator states induced either by interaction or by
dissipation.Comment: 5 pages, 5 figure
Optimisation of Fine Pitch Contactor and Test Board for QFN Package
Fine pitch contactor describes a contactor with smaller air gap between the contact pins. It is used for testing small portable devices. This work presents the optimised way of designing the 0.4 mm pitch contactor and test board for QFN package. The signal integrity of fine pitch test contactor has become a concern due to the small air-gap between the pins that leads to signal crosstalk and impedance mismatch issues. The same challenge had been seen when designing the fine pitch test board because of the requirement to meet 0.4 mm pitch for typical hand-held devices. It restricts the trace routing with typical design rules at the contactor mounting area due to the limited spaces. This would bring to impedance discontinuity and crosstalk effect. Therefore, optimised design rules on the fine pitch contactor and test board are necessary. Full-wave modelling and system level simulation were demonstrated to study the fine pitch design rules. While the full-wave modelling was to construct the contactor and test board components, the system level simulation was intended to study the signal transmission when propagating from one component to another. Overall, designing the fine pitch contactor requires extra study on the signal integrity and layout design. This paper presents a method to study and design the fine pitch contactor design. It reports the test board to achieve minimum losses and distortion test system for functional testing. Our simulation results for finepitch contactor model show that the return loss is less than 12 dB at 4 GHz
Enhanced ferroelectric and piezoelectric properties in doped lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 thin films
Doping effects with respect to the electrical properties of morphotropic phase boundary Bi0.5Na0.50.94Ba0.06TiO3 thin films epitaxially grown on CaRuO3 electroded LaAlO30.3Sr2AlTaO60.35 (001) substrates were investigated. Substantial enhancement of ferroelectricity and piezoelectricity has been achieved in La+Ce codoped films with a remanent polarization Pr of 29.5 C/cm2 and a remanent piezoelectric coefficient d33f of 31 pm/V, whereas Mn doping seems more favorite to reduce the leakage current by two order of magnitude. Both doped films exhibited diodelike I-V characteristics, which are correlated with resistance switching effect
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