Electron-phonon interaction via Pekar mechanism in nanostructures

We consider an electron-acoustic phonon coupling mechanism associated with the dependence of crystal dielectric permittivity on the strain (the so-called Pekar mechanism) in nanostructures characterized by strong confining electric fields. The efficiency of Pekar coupling is a function of both the absolute value and the spatial distribution of the electric field. It is demonstrated that this mechanism exhibits a phonon wavevector dependence similar to that of piezoelectricity and must be taken into account for electron transport calculations in an extended field distribution. In particular, we analyze the role of Pekar coupling in energy relaxation in silicon inversion layers. Comparison with the recent experimental results is provided to illustrate its potential significance

Mesoscopic fluctuations of the ground state spin of a small metal particle

We study the statistical distribution of the ground state spin for an ensemble of small metallic grains, using a random-matrix toy model. Using the Hartree Fock approximation, we find that already for interaction strengths well below the Stoner criterion there is an appreciable probability that the ground state has a finite, nonzero spin. Possible relations to experiments are discussed.Comment: 4 pages, RevTeX; 1 figure included with eps

Absence of bimodal peak spacing distribution in the Coulomb blockade regime

Using exact diagonalization numerical methods, as well as analytical arguments, we show that for the typical electron densities in chaotic and disordered dots the peak spacing distribution is not bimodal, but rather Gaussian. This is in agreement with the experimental observations. We attribute this behavior to the tendency of an even number of electrons to gain on-site interaction energy by removing the spin degeneracy. Thus, the dot is predicted to show a non trivial electron number dependent spin polarization. Experimental test of this hypothesis based on the spin polarization measurements are proposed.Comment: 13 pages, 3 figures, accepted for publication in PRL - a few small change

Density Modulations and Addition Spectra of Interacting Electrons in Disordered Quantum Dots

We analyse the ground state of spinless fermions on a lattice in a weakly disordered potential, interacting via a nearest neighbour interaction, by applying the self-consistent Hartree-Fock approximation. We find that charge density modulations emerge progressively when r_s >1, even away from half-filling, with only short-range density correlations. Classical geometry dependent "magic numbers" can show up in the addition spectrum which are remarkably robust against quantum fluctuations and disorder averaging.Comment: 4 pages, 3 eps figure

Thermodynamic magnetization of a strongly correlated two-dimensional electron system

We measure thermodynamic magnetization of a low-disordered, strongly correlated two-dimensional electron system in silicon. Pauli spin susceptibility is observed to grow critically at low electron densities - behavior that is characteristic of the existence of a phase transition. A new, parameter-free method is used to directly determine the spectrum characteristics (Lande g-factor and the cyclotron mass) when the Fermi level lies outside the spectral gaps and the inter-level interactions between quasiparticles are avoided. It turns out that, unlike in the Stoner scenario, the critical growth of the spin susceptibility originates from the dramatic enhancement of the effective mass, while the enhancement of the g-factor is weak and practically independent of the electron density.Comment: As publishe

On the computation of zone and double zone diagrams

Classical objects in computational geometry are defined by explicit relations. Several years ago the pioneering works of T. Asano, J. Matousek and T. Tokuyama introduced "implicit computational geometry", in which the geometric objects are defined by implicit relations involving sets. An important member in this family is called "a zone diagram". The implicit nature of zone diagrams implies, as already observed in the original works, that their computation is a challenging task. In a continuous setting this task has been addressed (briefly) only by these authors in the Euclidean plane with point sites. We discuss the possibility to compute zone diagrams in a wide class of spaces and also shed new light on their computation in the original setting. The class of spaces, which is introduced here, includes, in particular, Euclidean spheres and finite dimensional strictly convex normed spaces. Sites of a general form are allowed and it is shown that a generalization of the iterative method suggested by Asano, Matousek and Tokuyama converges to a double zone diagram, another implicit geometric object whose existence is known in general. Occasionally a zone diagram can be obtained from this procedure. The actual (approximate) computation of the iterations is based on a simple algorithm which enables the approximate computation of Voronoi diagrams in a general setting. Our analysis also yields a few byproducts of independent interest, such as certain topological properties of Voronoi cells (e.g., that in the considered setting their boundaries cannot be "fat").Comment: Very slight improvements (mainly correction of a few typos); add DOI; Ref [51] points to a freely available computer application which implements the algorithms; to appear in Discrete & Computational Geometry (available online

On the Electron-Electron Interactions in Two Dimensions

In this paper, we analyze several experiments that address the effects of electron-electron interactions in 2D electron (hole) systems in the regime of low carrier density. The interaction effects result in renormalization of the effective spin susceptibility, effective mass, and g*-factor. We found a good agreement among the data obtained for different 2D electron systems by several experimental teams using different measuring techniques. We conclude that the renormalization is not strongly affected by the material or sample-dependent parameters such as the potential well width, disorder (the carrier mobility), and the bare (band) mass. We demonstrate that the apparent disagreement between the reported results on various 2D electron systems originates mainly from different interpretations of similar "raw" data. Several important issues should be taken into account in the data processing, among them the dependences of the effective mass and spin susceptibility on the in-plane field, and the temperature dependence of the Dingle temperature. The remaining disagreement between the data for various 2D electron systems, on one hand, and the 2D hole system in GaAs, on the other hand, may indicate more complex character of electron-electron interactions in the latter system.Comment: Added refs; corrected typos. 19 pages, 7 figures. To be published in: Chapter 19, Proceedings of the EURESCO conference "Fundamental Problems of Mesoscopic Physics ", Granada, 200

Ground-state energy and spin in disordered quantum dots

We investigate the ground-state energy and spin of disordered quantum dots using spin-density-functional theory. Fluctuations of addition energies (Coulomb-blockade peak spacings) do not scale with average addition energy but remain proportional to level spacing. With increasing interaction strength, the even-odd alternation of addition energies disappears, and the probability of non-minimal spin increases, but never exceeds 50%. Within a two-orbital model, we show that the off-diagonal Coulomb matrix elements help stabilize a ground state of minimal spin.Comment: 10 pages, 2 figure

‘Get yourself some nice, neat, matching box files’: research administrators and occupational identity work

To date, qualitative research into occupational groups and cultures within academia has been relatively scarce, with an almost exclusive concentration upon teaching staff within universities and colleges. This article seeks to address this lacuna and applies the interactionist concept of ‘identity work’ in order to examine one specific group to date under-researched: graduate research administrators. This occupational group is of sociological interest as many of its members appear to span the putative divide between ‘academic’ and ‘administrative’ occupational worlds within higher education. An exploratory, qualitative research project was undertaken, based upon interviews with 27 research administrators. The study analyses how research administrators utilise various forms of identity work to sustain credible occupational identities, often in the face of considerable challenge from their academic colleagues

'Working out’ identity: distance runners and the management of disrupted identity

This article contributes fresh perspectives to the empirical literature on the sociology of the body, and of leisure and identity, by analysing the impact of long-term injury on the identities of two amateur but serious middle/long-distance runners. Employing a symbolic interactionist framework,and utilising data derived from a collaborative autoethnographic project, it explores the role of ‘identity work’ in providing continuity of identity during the liminality of long-term injury and rehabilitation, which poses a fundamental challenge to athletic identity. Specifically, the analysis applies Snow and Anderson’s (1995) and Perinbanayagam’s (2000) theoretical conceptualisations in order to examine the various forms of identity work undertaken by the injured participants, along the dimensions of materialistic, associative and vocabularic identifications. Such identity work was found to be crucial in sustaining a credible sporting identity in the face of disruption to the running self, and in generating momentum towards the goal of restitution to full running fitness and reengagement with a cherished form of leisure. KEYWORDS: identity work, symbolic interactionism, distance running, disrupted identit