Spin ice on the trillium lattice studied by Monte Carlo calculations

We study a local ferromagnetic Ising model for classical spins on the trillium lattice. The ground state of this model features two spins out(/in) and one spin in(/out) on each triangle, and leads to a macroscopic ground state degeneracy. Our Monte Carlo simulations find a ground state entropy intermediate to that of spin ice on the kagome and pyrochlore lattices, suggesting that trillium spin ice is highly frustrated. To motivate the search for trillium spin ice, we calculate the magnetic susceptibility and structure factor. We note the qualitative resemblance of the susceptibility to previously published work on EuPtSi, which features local moments on the trillium lattice.Comment: 8 pages, 6 figure

A microscopic model for spiral ordering along (110) on the MnSi lattice

We study an extended Heisenberg model on the MnSi lattice. In the cubic B20 crystal structure of MnSi, Mn atoms form lattices of of corner-shared equilateral triangles. We find an ubiquitous spiral ordering along (110) for J1 0, where J1, J2, and J3 are 1st, 2nd and 3rd nearest neighbor Heisenberg interactions, respectively. While the ordering direction of (110) is reasonably robust to the presence of the Dzyaloshinskii-Moriya interaction, it can be shifted to the (111) direction with the introduction of a magnetic anisotropy term for small J2/|J1|. We discuss the possible relevance of these results to the partially ordered state recently reported in MnSi.Comment: 5 pages, 4 figure

Integration of a resonant tunneling diode and an optical communications laser

We report on the first integration of a resonant tunneling diode and an optical communications laser operating at around 1.5 /spl μm. We demonstrate its low-frequency bistable operation and model its electrical characteristics

A Review of Rail Research Relevant to the Case for Increased Rail Investment.

The purpose of this paper is to provide a review of rail transport research which has a bearing on the case of increased rail investment. The paper focuses on research which has been conducted on the demand for rail travel, both passenger and freight, rather than the supply side or new technology. The aim is to identify where we believe there to be significant gaps in knowledge and key areas in which further research is required are outlined. The paper deals with the following issues: the investment and funding mechanisms that currently exist for rail; the extent to which changes in the fare and service quality of rail affect the demand for rail travel and also the demand for air and road travel; the environmental and congestion benefits of diverting traffic from road and air to rail; and the links between rail investment and economic development. Where appropriate, the discussion considers inter-urban travel, suburban travel, light rail transit and freight transport separately

Concentration dependent interdiffusion in InGaAs/GaAs as evidenced by high resolution x-ray diffraction and photoluminescence spectroscopy

Article copyright 2005 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The article appeared in Journal of Applied Physics 97, 013536 (2005) and may be found at

Beating of exciton-dressed states in a single semiconductor InGaAs/GaAs quantum dot

We report picosecond control of excitonic dressed states in a single semiconductor quantum dot. A strong laser pulse couples the exciton and biexciton states, to form an Autler-Townes doublet of the neutral exciton transition. The Rabi-splitting, and hence the admixture of the dressed states follows the envelope of the picosecond control laser. We create a superposition of dressed states, and observe the resulting beat: a direct measurement of a Rabi oscillation in time delay rather than the usual power domain

Voltage controlled nuclear polarization switching in a single InGaAs quantum dot

Sharp threshold-like transitions between two stable nuclear spin polarizations are observed in optically pumped individual InGaAs self-assembled quantum dots embedded in a Schottky diode when the bias applied to the diode is tuned. The abrupt transitions lead to the switching of the Overhauser field in the dot by up to 3 Tesla. The bias-dependent photoluminescence measurements reveal the importance of the electron-tunneling-assisted nuclear spin pumping. We also find evidence for the resonant LO-phonon-mediated electron co-tunneling, the effect controlled by the applied bias and leading to the reduction of the nuclear spin pumping rate.Comment: 5 pages, 2 figures, submitted to Phys Rev

The role of high growth temperature GaAs spacer layers in 1.3-/spl mu/m In(Ga)As quantum-dot lasers

We investigate the mechanisms by which high growth temperature spacer layers (HGTSLs) reduce the threshold current of 1.3-/spl mu/m emitting multilayer quantum-dot lasers. Measured optical loss and gain spectra are used to characterize samples that are nominally identical except for the HGTSL. We find that the use of the HGTSL leads to the internal optical mode loss being reduced from 15 /spl plusmn/ 2 to 3.5 /spl plusmn/ 2 cm/sup -1/, better defined absorption features, and more absorption at the ground state resulting from reduced inhomogenous broadening and a greater dot density. These characteristics, together with a reduced defect density, lead to greater modal gain at a given current density