4,710 research outputs found
Quantum Spin Hall Insulator State in HgTe Quantum Wells
Recent theory predicted that the Quantum Spin Hall Effect, a fundamentally
novel quantum state of matter that exists at zero external magnetic field, may
be realized in HgTe/(Hg,Cd)Te quantum wells. We have fabricated such sample
structures with low density and high mobility in which we can tune, through an
external gate voltage, the carrier conduction from n-type to the p-type,
passing through an insulating regime. For thin quantum wells with well width d
< 6.3 nm, the insulating regime shows the conventional behavior of vanishingly
small conductance at low temperature. However, for thicker quantum wells (d >
6.3 nm), the nominally insulating regime shows a plateau of residual
conductance close to 2e^2/h. The residual conductance is independent of the
sample width, indicating that it is caused by edge states. Furthermore, the
residual conductance is destroyed by a small external magnetic field. The
quantum phase transition at the critical thickness, d = 6.3 nm, is also
independently determined from the magnetic field induced insulator to metal
transition. These observations provide experimental evidence of the quantum
spin Hall effect.Comment: 16 pages, 5 figure
Dielectric Function of Diluted Magnetic Semiconductors in the Infrared Regime
We present a study of the dielectric function of metallic (III,Mn)V diluted
magnetic semiconductors in the infrared regime. Our theoretical approach is
based on the kinetic exchange model for carrier induced (III,Mn)V
ferromagnetism. The dielectric function is calculated within the random phase
approximation and, within this metallic regime, we treat disorder effects
perturbatively and thermal effects within the mean field approximation. We also
discuss the implications of this calculations on carrier concentration
measurements from the optical f-sum rule and the analysis of plasmon-phonon
coupled modes in Raman spectra.Comment: 6 pages, 6 figures include
Spatial effects of Fano resonance in local tunneling conductivity in vicinity of impurity on semiconductor surface
We present the results of local tunneling conductivity spatial distribution
detailed theoretical investigations in vicinity of impurity atom for a wide
range of applied bias voltage. We observed Fano resonance in tunneling
conductivity resulting from interference between resonant tunneling channel
through impurity energy level and direct tunneling channel between the
tunneling contact leads. We have found that interference between tunneling
channels strongly modifies form of tunneling conductivity measured by the
scanning tunneling microscopy/spectroscopy (STM/STS) depending on the distance
value from the impurity.Comment: 4 pages, 3 figure
Program on stimulating operational private sector use of Earth observation satellite information
Ideas for new businesses specializing in using remote sensing and computerized spatial data systems were developd. Each such business serves as an 'information middleman', buying raw satellite or aircraft imagery, processing these data, combining them in a computer system with customer-specific information, and marketing the resulting information products. Examples of the businesses the project designed are: (1) an agricultural facility site evaluation firm; (2) a mass media grocery price and supply analyst and forecaster; (3) a management service for privately held woodlots; (4) a brokerage for insulation and roofing contractors, based on infrared imagery; (5) an expanded real estate information service. In addition, more than twenty-five other commercially attractive ideas in agribusiness, forestry, mining, real estate, urban planning and redevelopment, and consumer information were created. The commercial feasibility of the five business was assessed. This assessment included market surveys, revenue projections, cost analyses, and profitability studies. The results show that there are large and enthusiastic markets willing to pay for the services these businesses offer, and that the businesses could operate profitably
Detecting dynamic system regime boundaries with Fisher information: the case of ecosystems
The direct measurement of the resilience (resistance to disturbances) of an ecosystemâs current regime (or âalternative stable stateâ) remains a key concern for managing human impacts on these ecosystems and their risk of collapse. Approaches which utilize statistics or information theory have demonstrated utility in identifying regime boundaries. Here, we use Fisher information to establish the limits of the resilience of a dynamic regime of a predatorâprey system. This is important because previous studies using Fisher information focused on detecting whether a regime change has occurred, whereas here we are interested in determining how much an ecological system can vary its properties without a regime change occurring. We illustrate the theory with simple two species systems. We apply it first to a predatorâprey model and then to a 60-year wolfâmoose population dataset from Isle Royale National Park in Michigan, USA. We assess the resilience boundaries and the operating range of a systemâs parameters without a regime change from entirely new criteria for Fisher information, oriented toward regime stability. The approach allows us to use system measurements to determine the shape and depth of the âcupâ as defined by the broader resilience concept
Conductance plateau in quantum spin transport through an interacting quantum dot
Quantum spin transport is studied in an interacting quantum dot. It is found
that a conductance "plateau" emerges in the non-linear charge conductance by a
spin bias in the Kondo regime. The conductance plateau, as a complementary to
the Kondo peak, originates from the strong electron correlation and exchange
processes in the quantum dot, and can be regarded as one of the characteristics
in quantum spin transport.Comment: 5 pages, 5 figure
A large-deviations principle for all the cluster sizes of a sparse ErdĆsâRĂ©nyi graph
Let (Formula presented.) be the ErdĆsâRĂ©nyi graph with connection probability (Formula presented.) as N â â for a fixed t â (0, â). We derive a large-deviations principle for the empirical measure of the sizes of all the connected components of (Formula presented.), registered according to microscopic sizes (i.e., of finite order), macroscopic ones (i.e., of order N), and mesoscopic ones (everything in between). The rate function explicitly describes the microscopic and macroscopic components and the fraction of vertices in components of mesoscopic sizes. Moreover, it clearly captures the well known phase transition at t = 1 as part of a comprehensive picture. The proofs rely on elementary combinatorics and on known estimates and asymptotics for the probability that subgraphs are connected. We also draw conclusions for the strongly related model of the multiplicative coalescent, the MarcusâLushnikov coagulation model with monodisperse initial condition, and its gelation phase transition
Program on stimulating operational private sector use of Earth observation satellite data
There are no author-identified significant results in this report
Introduction: Celebrating the Mound City Bar Association Centennial: Looking Back, Leading Forward
In 2022, the Mound City Bar Association in St. Louis, one of the first Black bar associations in the country, celebrates its 100th anniversary. In this volume of the Washington University Journal of Law & Policy, distinguished authors look back at a century of contributions of Mound City Bar Association lawyers, judges, and allies, documenting their efforts to eliminate racial discrimination and break down barriers to equal justice. The volume is a testament to the work of countless individuals in the fight for civil rights since the beginning of the association in 1922. The authors also anticipate and examine the challenges ahead and the work yet to be done to achieve equal justice for all in our city, the region, and the country in the years to come
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