Spin Hall Effect and Spin Orbit coupling in Ballistic Nanojunctions

We propose a new scheme of spin filtering based on nanometric crossjunctions in the presence of Spin Orbit interaction, employing ballistic nanojunctions patterned in a two-dimensional electron gas. We demonstrate that the flow of a longitudinal unpolarized current through a ballistic X junction patterned in a two-dimensional electron gas with Spin Orbit coupling (SOC) induces a spin accumulation which has opposite signs for the two lateral probes. This spin accumulation, corresponding to a transverse pure spin current flowing in the junction, is the main observable signature of the spin Hall effect in such nanostructures. We benchmark the effects of two different kinds of Spin Orbit interactions. The first one ($\alpha$-SOC) is due to the interface electric field that confines electrons to a two-dimensional layer, whereas the second one ($\beta$-SOC) corresponds to the interaction generated by a lateral confining potential.Comment: 6 pages, 3 figure

Tunable control of the bandwidth and frequency correlations of entangled photons

We demonstrate experimentally a new technique to control the bandwidth and the type of frequency correlations (correlation, anticorrelation, and even uncorrelation) of entangled photons generated by spontaneous parametric downconversion. The method is based on the control of the group velocities of the interacting waves. This technique can be applied in any nonlinear medium and frequency band of interest. It is also demonstrated that this technique helps enhance the quality of polarization entanglement even when femtosecond pulses are used as a pump.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let

Effective interactions between inclusions in complex fluids driven out of equilibrium

The concept of fluctuation-induced effective interactions is extended to systems driven out of equilibrium. We compute the forces experienced by macroscopic objects immersed in a soft material driven by external shaking sources. We show that, in contrast with equilibrium Casimir forces induced by thermal fluctuations, their sign, range and amplitude depends on specifics of the shaking and can thus be tuned. We also comment upon the dispersion of these shaking-induced forces, and discuss their potential application to phase ordering in soft-materials.Comment: 10 pages, 8 figures, to appear in PR

Resonances and resonant frequencies for a class of nonlinear systems

Resonant phenomena for a class of nonlinear systems, which can be described by a SDOF model with a polynomial type nonlinear stiffness, are investigated using Nonlinear Output Frequency Response Functions (NOFRFs). The concepts of resonance and resonant frequencies are proposed for the first time for a class of nonlinear systems. The effects of damping on the resonances and resonant frequencies are also analyzed. These results produce a novel interpretation of energy transfer phenomena in this class of nonlinear systems and show how the damping effect influences the system resonant frequencies and amplitudes. The results are important for the design and fault diagnosis of mechanical systems and structures which can be described by the SDOF nonlinear model

Modified Combline Filter for A Compact Size

Bandpass filters are widely used in microwave systems. And miniaturized bandpass filters are required to reduce the cost of a wireless communication system. Therefore, many prototypes have been studied to meet this requirement. The conventional comb-line filter is one of the so many types of proposed size-reduced filters. In this thesis, we propose a modified comb-line filter using a combination of end shorted parallel coupled lines and lumped capacitors. Using the above structure, the electrical length of the parallel coupled lines in the modified comb-line filter, which determines the size of a comb-line filter, can be reduced to even a few degrees, resulting in a much smaller circuit area. Inter-stage connecting lines have been added to connect the neighboring resonators for the suppression of unwanted coupling. The designed comb-line filter also shows a wide upper stopband. Design equations and method will be fully explained in this thesis. Measured results of a fabricated filter centered at 400 MHz show good agreement with the theoretical predications.Chapter 1 Introduction = 1 1.1 An introduction to Comb-line filters = 2 1.2 Research Contents = 4 Chapter 2 Miniaturization of the Quarter-wavelength Transmission Line = 5 2.1 Introduction = 5 2.2 Size-reducing method of the λ/4 transmission line = 7 Chapter 3 Bandpass Filter Design Theory = 15 3.1 Introduction = 15 3.2 Size-reduced Bandpass filter = 16 Chapter 4 Fabrication and Measurement = 25 4.1 EM simulation using HFSS = 25 4.2 Fabrication and Measurement = 31 Chapter 5 Conclusion = 37 References = 38 Acknowledgement = 4

Frequency domain energy transfer properties of bilinear oscillators under harmonic loadings

In this paper, the energy transfer phenomenon of bilinear oscillators in the frequency domain is analyzed using the new concept of Nonlinear Output Frequency Response Functions (NOFRFs). The analysis provides insight into how new frequency generation can occur using bilinear oscillators, and reveals, for the first time, that it is the resonant frequencies of the NOFRFs that dominate the occurrence of this well-known nonlinear behaviour. The results are of significance for the design and fault diagnosis of mechanical systems and structures which can be described by a bilinear oscillator model