Tunneling Between Multimode Stacked Quantum Wires

Tunneling between vertically stacked quantum wires has been investigated. The wires are assumed to have the dimension perpendicular to the tunneling barrier much smaller than the other transverse dimension, so that only the lowest mode in such direction is to be taken into account, while many modes in the other direction are filled. A model with hard-wall confinement has been used for the investigation of the transport problem, and the tunneling conductance has been computed, via a recursive Green's functions procedure

Vertical-external-cavity surface-emitting lasers and quantum dot lasers

The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and also quantum information devices. In particular, in the field of semiconductor lasers, QDs were introduced as a superior alternative to quantum wells to suppress the temperature dependence of the threshold current in vertical-external-cavity surface-emitting lasers (VECSELs). In this work, a review of properties and development of semiconductor VECSEL devices and QD laser devices is given. Based on the features of VECSEL devices, the main emphasis is put on the recent development of technological approach on semiconductor QD VECSELs. Then, from the viewpoint of both single QD nanolaser and cavity quantum electrodynamics (QED), a single-QD-cavity system resulting from the strong coupling of QD cavity is presented. A difference of this review from the other existing works on semiconductor VECSEL devices is that we will cover both the fundamental aspects and technological approaches of QD VECSEL devices. And lastly, the presented review here has provided a deep insight into useful guideline for the development of QD VECSEL technology and future quantum functional nanophotonic devices and monolithic photonic integrated circuits (MPhICs).Comment: 21 pages, 4 figures. arXiv admin note: text overlap with arXiv:0904.369

Designing a Method for Measuring Magnetoresistance of Nanostructures

The ultimate intent of this research program is to produce nanosized magnetic tunneling junctions, and to study the physical properties of such devices. The physical phenomena of nanosized tunneling junctions are significantly different than that of currently popular micro-sized junctions. There is a considerable amount of work that must be done prior to producing these new junctions to ensure that good measurements can be carried out once the structures have been built. This thesis describes the efforts taken to design a measurement platform that will accurately measure tunneling magnetoresistance (TMR) in nanosized Magneto-tunneling Junctions (MTJ). The testing done with this system at various stages throughout the design and testing process confirm the expectations for the performance of the system. Voltage-current measurements can be performed on objects ranging from a few nanometers in size to micrometer sized. Traditional micro-sized MTJs have not been excluded in this design

Designing a Method for Measuring Magnetoresistance of Nanostructures

The ultimate intent of this research program is to produce nanosized magnetic tunneling junctions, and to study the physical properties of such devices. The physical phenomena of nanosized tunneling junctions are significantly different than that of currently popular micro-sized junctions. There is a considerable amount of work that must be done prior to producing these new junctions to ensure that good measurements can be carried out once the structures have been built. This thesis describes the efforts taken to design a measurement platform that will accurately measure tunneling magnetoresistance (TMR) in nanosized Magneto-tunneling Junctions (MTJ). The testing done with this system at various stages throughout the design and testing process confirm the expectations for the performance of the system. Voltage-current measurements can be performed on objects ranging from a few nanometers in size to micrometer sized. Traditional micro-sized MTJs have not been excluded in this design

Charge transport modulation by a redox supramolecular spin-filtering chiral crystal

The chirality induced spin selectivity (CISS) effect is a fascinating phenomena correlating molecular structure with electron spin-polarisation in excited state measurements. Experimental procedures to quantify the spin-filtering magnitude relies generally on averaging data sets, especially those from magnetic field dependent conductive-AFM. We investigate the underlying observed disorder in the IV spectra and the origin of spikes superimposed. We demonstrate and explain that a dynamic, voltage sweep rate dependent, phenomena can give rise to complex IV curves for chiral crystals of coronene bisimide. The redox group, able to capture localized charge states, acts as an impurity state interfering with a continuum, giving rise to Fano resonances. We introduce a novel mechanism for the dynamic transport which might also provide insight into the role of spin-polarization. Crucially, interference between charge localisation and delocalisation during transport may be important properties into understanding the CISS phenomena

Symmetry and Asymmetry in Quasicrystals or Amorphous Materials

About forty years after its discovery, it is still common to read in the literature that quasicrystals (QCs) occupy an intermediate position between amorphous materials and periodic crystals. However, QCs exhibit high-quality diffraction patterns containing a collection of discrete Bragg reflections at variance with amorphous phases. Accordingly, these materials must be properly regarded as long-range ordered materials with a symmetry incompatible with translation invariance. This misleading conceptual status can probably arise from the use of notions borrowed from the amorphous solids framework (such us tunneling states, weak interference effects, variable range hopping, or spin glass) in order to explain certain physical properties observed in QCs. On the other hand, the absence of a general, full-fledged theory of quasiperiodic systems certainly makes it difficult to clearly distinguish the features related to short-range order atomic arrangements from those stemming from long-range order correlations. The contributions collected in this book aim at gaining a deeper understanding on the relationship between the underlying structural order and the resulting physical properties in several illustrative aperiodic systems, including the border line between QCs and related complex metallic alloys, hierarchical superlattices, electrical transmission lines, nucleic acid sequences, photonic quasicrystals, and optical devices based on aperiodic order designs

Electron-correlation driven capture and release in double quantum dots

We recently predicted that the interatomic Coulombic electron capture (ICEC) process, a long-range electron correlation driven capture process, is achievable in gated double quantum dots (DQDs). In ICEC an incoming electron is captured by one QD and the excess energy is used to remove an electron from the neighboring QD. In this work we present systematic full three-dimensional electron dynamics calculations in quasi-one dimensional model potentials that allow for a detailed understanding of the connection between the DQD geometry and the reaction probability for the ICEC process. We derive an effective one-dimensional approach and show that its results compare very well with those obtained using the full three-dimensional calculations. This approach substantially reduces the computation times. The investigation of the electronic structure for various DQD geometries for which the ICEC process can take place clarify the origin of its remarkably high probability in the presence of two-electron resonances

Challenges in simulating light-induced processes in DNA

© 2016 by the authors; licensee MDPI, Basel, Switzerland. In this contribution, we give a perspective on the main challenges in performing theoretical simulations of photoinduced phenomena within DNA and its molecular building blocks. We distinguish the different tasks that should be involved in the simulation of a complete DNA strand subject to UV irradiation: (i) stationary quantum chemical computations; (ii) the explicit description of the initial excitation of DNA with light; (iii) modeling the nonadiabatic excited state dynamics; (iv) simulation of the detected experimental observable; and (v) the subsequent analysis of the respective results. We succinctly describe the methods that are currently employed in each of these steps. While for each of them, there are different approaches with different degrees of accuracy, no feasible method exists to tackle all problems at once. Depending on the technique or combination of several ones, it can be problematic to describe the stacking of nucleobases, bond breaking and formation, quantum interferences and tunneling or even simply to characterize the involved wavefunctions. It is therefore argued that more method development and/or the combination of different techniques are urgently required. It is essential also to exercise these new developments in further studies on DNA and subsystems thereof, ideally comprising simulations of all of the different components that occur in the corresponding experiments