Gate control of a quantum dot single-electron spin in realistic confining potentials: anisotropy effects

Among recent proposals for next-generation, non-charge-based logic is the notion that a single electron can be trapped and its spin can be manipulated through the application of gate potentials. In this paper, we present numerical simulations of such spins in single electron devices for realistic (asymmetric) confining potentials in two-dimensional electrostatically confined quantum dots. Using analytical and numerical techniques we show that breaking the in-plane rotational symmetry of the confining potential leads to a significant effect on the tunability of the g-factor with applied gate potentials. In particular, anisotropy extends the range of tunability to larger quantum dots.Comment: 7 pages, 13 figure

Mission At and From the Margins Patterns, Protagonists and Perspectives

It is our hope that these chapters, though fragmentary in nature, will provide glimpses of how the ‘margins’ can both inform and re-form missiological thought as we build further upon what has happened since Edinburgh 1910. These fragments are offered with the hope that they will not only feed and nourish but also provoke hunger for working towards God’s kingdom of justice and righteousness.https://scholar.csl.edu/edinburghcentenary/1016/thumbnail.jp

Role of Boron p-Electrons and Holes in Superconducting MgB2, and other Diborides: A Fully-Relaxed, Full-Potential Electronic Structure Study

We present the results of fully-relaxed, full-potential electronic structure calculations for the new superconductor MgB2, and BeB2, NaB2, and AlB2, using density-functional-based methods. Our results described in terms of (i) density of states (DOS), (ii) band-structure, and (iii) the DOS and the charge density around the Fermi energy EF, clearly show the importance of B p-band for superconductivity. In particular, we show that around EF, the charge density in MgB2, BeB2 and NaB2 is planar and is associated with the B plane. For BeB2 and NaB2, our results indicate qualitative similarities but significant quantitative differences in their electronic structure due to different lattice constants a and c.Comment: 4 pages, 4 figures, Submitted to Phys Rev. Lett. on March 6, 2001; resubmission on April 2

Compositional disorder and its influence on the structural, electronic and magnetic properties of MgC(Ni_{1-x}Co_{x})_{3} alloys using first-principles

First-principles, density-functional based electronic structure calculations are carried out for MgC(Ni_{1-x}Co_{x})_{3} alloys over the concentration range 0\leq x\leq1, using Korringa-Kohn-Rostoker coherent-potential approximation (KKR CPA) method in the atomic sphere approximation (ASA). The self-consistent calculations are used to study the changes as a function of x in the equation of state parameters, total and partial densities of states, magnetic moment and the on-site exchange interaction parameter. To study the magnetic properties as well as its volume dependence, fixed-spin moment calculations in conjunction with the phenomenological Landau theory are employed. The salient features that emerge from these calculations are (i) a concentration independent variation in the lattice parameter and bulk modulus at x~0.75 with an anomaly in the variation of the pressure derivative of bulk modulus, (ii) the fixed-spin moment based corrections to the overestimated magnetic ground state for 0.0\leq x\leq0.3 alloys, making the results consistent with the experiments, and (iii) the possibility of multiple magnetic states at x~0.75, which, however, requires further improvements in the calculations

Role of C in MgC_xNi_3 investigated from first principles

The influence of vacancies in the $C$ sub-lattice of $MgCNi_{3}$, on its structural, electronic and magnetic properties are studied by means of the density-functional based Korringa-Kohn-Rostoker Green's function method formulated in the atomic sphere approximation. Disorder is taken into account by means of coherent-potential approximation. Characterizations representing the change in the lattice properties include the variation in the equilibrium lattice constants, bulk modulus and pressure derivative of the bulk modulus, and that of electronic structure include the changes in the, total, partial and $\mathbf{k}$-resolved density of states. The incipient magnetic properties are studied by means of fixed-spin moment method of alloy theory, together in conjunction with the phenomenological Ginzburg-Landau equation for magnetic phase transition. The first-principles calculations reveal that due to the breaking of the $C$-$Ni$ bonds, some of the $Ni$ 3d states, which were lowered in energy due to strong hybridization, are transfered back to higher energies thereby increasing the itinerant character in the material. The Bloch spectral densities evaluated at the high symmetry points however reveal that the charge redistribution is not uniform over the cubic Brillouin zone, as new states are seen to be created at the $\Gamma$ point, while a shift in the states on the energy scale are seen at other high symmetry points

Ion Write Microthermotics: Programing Thermal Metamaterials at the Microscale.

Considerable advances in manipulating heat flow in solids have been made through the innovation of artificial thermal structures such as thermal diodes, camouflages, and cloaks. Such thermal devices can be readily constructed only at the macroscale by mechanically assembling different materials with distinct values of thermal conductivity. Here, we extend these concepts to the microscale by demonstrating a monolithic material structure on which nearly arbitrary microscale thermal metamaterial patterns can be written and programmed. It is based on a single, suspended silicon membrane whose thermal conductivity is locally, continuously, and reversibly engineered over a wide range (between 2 and 65 W/m·K) and with fine spatial resolution (10-100 nm) by focused ion irradiation. Our thermal cloak demonstration shows how ion-write microthermotics can be used as a lithography-free platform to create thermal metamaterials that control heat flow at the microscale

Effects of Disorder in FeSe : An Ab Initio Study

Using the coherent-potential approximation, we have studied the effects of excess Fe, Se-deficiency, and substitutions of S, Te on Se sub-lattice and Co, Ni and Cu on Fe sub-lattice in FeSe. Our results show that (i) a small amount of excess Fe substantially disorders the Fe-derived bands while Se-deficiency affects mainly the Se-derived bands, (ii) the substitution of S or Te enhances the possibility of Fermi surface nesting, specially in FeSe$_{0.5}$Te$_{0.5}$, in spite of disordering the Se-derived bands, (iii) the electron doping through Co, Ni or Cu disorders the system and pushes down the Fe-derived bands, thereby destroying the possibility of Fermi surface nesting. A comparison of these results with the rigid-band, virtual-crystal and supercell approximations reveals the importance of describing disorder with the coherent-potential approximation.Comment: Redone VCA calculations, and some minor changes. (Accepted for publication in Journal of Physics:Condensed Matter

A first-principles comparison of the electronic properties of MgC_{y}Ni_{3} and ZnC_{y}Ni_{3} alloys

First-principles, density-functional-based electronic structure calculations are employed to study the changes in the electronic properties of ZnC_{y}Ni_{3} and MgC_{y}Ni_{3} using the Korringa-Kohn-Rostoker coherent-potential approximation method in the atomic sphere approximation (KKR-ASA CPA). As a function of decreasing C at%, we find a steady decrease in the lattice constant and bulk modulus in either alloys. However, the pressure derivative of the bulk modulus displays an opposite trend. Following the Debye model, which relates the pressure derivative of the bulk modulus with the average phonon frequency of the crystal, it can thus be argued that ZnCNi_{3} and its disordered alloys posses a different phonon spectra in comparison to its MgCNi_{3} counterparts. This is further justified by the marked similarity we find in the electronic structure properties such as the variation in the density of states and the Hopfield parameters calculated for these alloys. The effects on the equation of state parameters and the density of states at the Fermi energy, for partial replacement of Mg by Zn are also discussed.Comment: 19 pages, 15 figure

Correlations due to localization in quantum eigenfunctions of disordered microwave cavities

Non-universal correlations due to localization are observed in statistical properties of experimental eigenfunctions of quantum chaotic and disordered microwave cavities. Varying energy {E} and mean free path {l} enable us to experimentally tune from localized to delocalized states. Large level-to-level Inverse Participation Ratio (IPR I_{2}) fluctuations are observed for the disordered billiards, whose distribution is strongly asymmetric about . The density auto-correlations of eigenfunctions are shown to decay exponentially and the decay lengths are experimentally determined. All the results are quantitatively consistent with calculations based upon nonlinear sigma-models.Comment: 4 pages, LaTex, 5 .jpg figures. This paper with 5 embedded postscript figures available (PS,PDF) at http://sagar.physics.neu.edu/preprints