Fractional quantum Hall effect in CdTe

The fractional quantum Hall (FQH) effect is reported in a high mobility CdTe quantum well at mK temperatures. Fully-developed FQH states are observed at filling factor 4/3 and 5/3 and are found to be both spin-polarized ground state for which the lowest energy excitation is not a spin-flip. This can be accounted for by the relatively high intrinsic Zeeman energy in this single valley 2D electron gas. FQH minima are also observed in the first excited (N=1) Landau level at filling factor 7/3 and 8/3 for intermediate temperatures.Comment: Submitte

The Network of Early Modern Printers and Its Impact on the Evolution of Scientific Knowledge: Automatic Detection of Awareness Relationships

This work describes a computational method for reconstructing clusters of social relationships among early modern printers and publishers, the most determinant agents for the process of transformation of scientific knowledge. The method is applied to a dataset retrieved from the Sphaera corpus, a collection of 359 editions of textbooks used at European universities and produced between the years 1472 and 1650. The method makes use of standard bibliographic data and fingerprints; social relationships are defined as “awareness relationships”. The historical background is constituted of the production and economic practices of early modern printers and publishers in the academic book market. The work concludes with empirically validating historical case studies, their historical interpretation, and suggestions for further improvements by utilizing machine learning technologies

SU(2)xSU(2) nonlocal quark model with confinement

The nonlocal version of the SU(2)xSU(2) symmetric four-quark interaction of the NJL type is considered. Each of the quark lines contains the form factors. These form factors remove the ultraviolet divergences in quark loops. The additional condition on quark mass function m(p) ensures the absence of the poles in the quark propagator(quark confinement). The constituent quark mass m(0) is expressed thought the cut-off parameter Lambda, m(0)=Lambda=340 MeV in the chiral limit. These parameters are fixed by the experimental value of the weak pion decay and allow us to describe the mass of the light scalar meson, strong decay rho -> pi pi and D/S ratio in the decay a_1 -> rho pi in satisfactory agreement with experimental data.Comment: 8 pages, 1 figure

Triplet-singlet relaxation in semiconductor single and double quantum dots

We study the triplet-singlet relaxation in two-electron semiconductor quantum dots. Both single dots and vertically coupled double dots are discussed. In our work, the electron-electron Coulomb interaction, which plays an important role in the electronic structure, is included. The spin mixing is caused by spin-orbit coupling which is the key to the triplet-singlet relaxation. We show that the selection rule widely used in the literature is incorrect unless near the crossing/anticrossing point in single quantum dots. The triplet/singlet relaxation in double quantum dots can be markedly changed by varying barrier height, inter-dot distance, external magnetic field and dot size.Comment: 7 pages, 4 figures, PRB in pres

Vector Mesons on the Light Front

We apply the light-front quantization to the Nambu--Jona-Lasinio model with the vector interaction, and compute vector meson's mass and light-cone wavefunction in the large N limit. Following the same procedure as in the previous analyses for scalar and pseudo-scalar mesons, we derive the bound-state equations of a q-qbar system in the vector channel. We include the lowest order effects of the vector interaction. The resulting transverse and longitudinal components of the bound-state equation look different from each other. But eventually after imposing an appropriate cutoff, one finds these two are identical, giving the same mass and the same (spin-independent) light-cone wavefunction. Mass of the vector meson decreases as one increases the strength of the vector interaction.Comment: 11 pages, 3 figures, discussion on the cutoff scheme changed, Fig.3 replaced, and one reference adde

Realistic Tight Binding Model for the Electronic Structure of II-VI Semiconductors

We analyze the electronic structure of group II-VI semiconductors obtained within LMTO approach in order to arrive at a realistic and minimal tight binding model, parameterized to provide an accurate description of both valence and conduction bands. It is shown that a nearest-neighbor $sp^3d^5$ model is fairly sufficient to describe to a large extent the electronic structure of these systems over a wide energy range, obviating the use of any fictitious $s^*$ orbital. The obtained hopping parameters obey the universal scaling law proposed by Harrison, ensuring transferability to other systems. Furthermore, we show that certain subtle features in the bonding of these compounds require the inclusion of anion-anion interactions in addition to the nearest-neighbor cation-anion interactions.Comment: 9 pages, 9 figure

First-principles calculations of the threedimensional structure and intrinsic defects in trans-polyacetylene

We report a first-principles, local-density-functional (LDA) calculation of the electronic structure of crystalline, three-dimensional (3D) trans-(CH)". For the perfect crystal, we find a brokensymmetry ground state having P2&/a space-group symmetry, corresponding to in-phase dimerization on neighboring chains within the unit cell. We show that in this structure the interchain couplings, although weak, lead to an asymmetry between the valence and conduction bands and, more importantly, give 3D character to the electronic band-edge states. We investigate several additional aspects of the electronic structure of the perfect crystal, including self-consistent optimization of the ions in the unit cell, spin polarization and electronic charge densities, interchain electron-phonon interactions, and the density of states. To study intrinsic defects in trans-(CH)", we map our LDA results onto a multi-orbital, tight-binding model; this mapping preserves very accurately all the electronic-structure properties of the full calculation. Using a Koster-Slater Green-function technique, we are able to examine both (shallow) polaronlike and (deep) bipolaronlike lattice distortions corresponding to localized defects. We find that the 3D character of the electronic band-edge states strongly suppresses the formation of the self-trapped, localized defects characteristic of the 1D models, destabilizing polarons and possibly bipolarons as well in perfectly ordered 3D trans-(CH)". To establish a connection with earlier work, we demonstrate that by artificially decreasing interchain effects and/or increasing the intrachain electron-phonon coupling we can cause polarons and bipolarons to form. We examine the agreement of our results for the idealized perfectly crystalline material with experimental results on real samples of trans-(CH)"and conclude with suggestions for future work, both theoretical and experimental