Checkerboard order in the t--J model on the square lattice

We propose that the inhomogeneous patterns seen by STM in some underdoped superconducting cuprates could be related to a bond-order-wave instability of the staggered flux state, one of the most studied "normal" state proposed to compete with the d-wave RVB superconductor. A checkerboard pattern is obtained by a Gutzwiller renormalized mean-field theory of the t-J model for doping around 1/8. It is found that the charge modulation is always an order of magnitude smaller than the bond-order modulations. This is confirmed by an exact optimization of the wavefunction by a variational Monte Carlo scheme. The numerical estimates of the order parameters are however found to be strongly reduced w.r.t their mean-field values

Quantum transport signatures of chiral edge states in Sr2_2RuO4_4

We investigate transport properties of a double quantum dot based Cooper pair splitter, where the superconducting lead consists of Sr$_2$RuO$_4$. The proposed device can be used to explore the symmetry of the superconducting order parameter in Sr$_2$RuO$_4$ by testing the presence of gapless chiral edge states, which are predicted to exist if the bulk superconductor is described by a chiral $p$--wave state. The odd orbital symmetry of the bulk order parameter ensures that we can realize a regime where the electrons tunneling into the double dot system come from the chiral edge states and thereby leave their signature in the conductance. The proposed Cooper pair splitter has the potential to probe order parameters in unconventional superconductors.Comment: 5 page

Multiple layer local oxidation for fabricating semiconductor nanostructures

Coupled semiconductor nanostructures with a high degree of tunability are fabricated using local oxidation with a scanning force microscope. Direct oxidation of the GaAs surface of a Ga[Al]As heterostructure containing a shallow two-dimensional electron gas is combined with the local oxidation of a thin titanium film evaporated on top. A four-terminal quantum dot and a double quantum dot system with integrated charge readout are realized. The structures are tunable via in-plane gates formed by isolated regions in the electron gas and by mutually isolated regions of the Ti film acting as top gates. Coulomb blockade experiments demonstrate the high quality of this fabrication process.Comment: 3 pages, 3 figure

Bond order wave instabilities in doped frustrated antiferromagnets: "Valence bond solids" at fractional filling

We explore both analytically and numerically the properties of doped t-J models on a class of highly frustrated lattices, such as the kagome and the pyrochlore lattice. Focussing on a particular sign of the hopping integral and antiferromagnetic exchange, we find a generic symmetry breaking instability towards a twofold degenerate ground state at a fractional filling below half filling. These states show modulated bond strengths and only break lattice symmetries. They can be seen as a generalization of the well-known valence bond solid states to fractional filling.Comment: slightly shortened and reorganized versio

Screw- and nail-gluing techniques for wood composite structures

Composite systems enhance the structural capacity and reliability of wood solutions for structures. With today engineered wood products and structural adhesives, high performing structures can be constructed. Hybrid assembly techniques that combine mechanical fasteners and an adhesive (screw- and nailgluing techniques) allow manufacturing large dimension composite structures with reasonable infrastructure. They also give full composite properties to the interlayers. Furthermore, these hybrid connections can experience ductility. This paper presents a research on small-scale glued assemblies which were manufactured using screw- and nail-gluing techniques. It discusses qualitative and quantitative analyses that confirmed the full-composite properties and ductility of the interlayers. The analyses also show that superposing the behaviour of both connectors is reasonable to predict the strength and slip modulus of hybrid connections. © 2007 Taylor & Francis Group, London

Understanding the composite characteristics of stressed-skin panels

The composite properties of stressed-skin panel (SSP) systems are characterised by the interaction ? composite action ? and the portion of the sheathing acting with the joists ? the tributary width. A discussion on the tributary width forms the focus of this paper. An analysis, which has been conducted considering the pattern of the strain distribution in the sheathing(s), is presented. It uses laboratory data of a major research project conducted at the University of Technology, Sydney, between 2002 and 2007 (Gerber 2007). This analysis indicates that under strict conditions, in particular structurally glued interlayers, a large portion of the sheathing contributes to the structural behaviour of SSP structures. A better use of the mechanical properties of the panels is also achieved. This paper also presents an analysis on the effects of discontinuities in the sheathing. It has been identified that such event causes a significant reduction of the sheathing contribution

Quasiparticle Dynamics in the Kondo Lattice Model at Half Filling

We study spectral properties of quasiparticles in the Kondo lattice model in one and two dimensions including the coherent quasiparticle dispersions, their spectral weights and the full two-quasiparticle spectrum using a cluster expansion scheme. We investigate the evolution of the quasiparticle band as antiferromagnetic correlations are enhanced towards the RKKY limit of the model. In both the 1D and the 2D model we find that a repulsive interaction between quasiparticles results in a distinct antibound state above the two-quasiparticle continuum. The repulsive interaction is correlated with the emerging antiferromagnetic correlations and can therefore be associated with spin fluctuations. On the square lattice, the antibound state has an extended s-wave symmetry.Comment: 8 pages, 11 figure

In Situ Treatment of a Scanning Gate Microscopy Tip

In scanning gate microscopy, where the tip of a scanning force microscope is used as a movable gate to study electronic transport in nanostructures, the shape and magnitude of the tip-induced potential are important for the resolution and interpretation of the measurements. Contaminations picked up during topography scans may significantly alter this potential. We present an in situ high-field treatment of the tip that improves the tip-induced potential. A quantum dot was used to measure the tip-induced potential.Comment: 3 pages, 1 figure, minor changes to fit published versio

Computer Simulations of Timber-stressed Skin Panels Using Finite Elements

A Finite Element Model (FEM) can provide a helpful and accurate tool for acquiring a better understanding of complex structures such stressed skin panel (SSP) systems and can contribute towards saving costly experiments. Because SSP constructions are highly complex, orthotropic, statically indeterminate and multi-layer assemblies and their members are orthotropic, and have viscoelastic properties and non-linear behaviour under certain conditions, accommodating SSP systems into a FEM is an arduous task and inevitably represents an idealisation of the physical structures