The theory of the "0.7 anomaly" in quantum point contacts

The phenomenology of the "0.7 anomaly" in quantum point contacts is fully explained in terms of a quasi-localized state, which forms as the point contact opens up. Detailed numerical calculations within spin-density functional theory indeed con rm the emergence of such a state. Quantitative calculations of the conductance and the noise are obtained using a model based on these observations, and are in excellent agreement with existing experimental observations.Comment: A summary paper, to be included in JPCM Special Issue on 0.7 Featur

The Beira Blockade

A RLJ on the UN economic blockade imposed on the rebel Rhodesia government and its implication at international law.This is the third in Mr. Wharam’s series of articles on the legal implications of U.D.I. (See [1967] C.L.J. 189 and 1969 R.L.J. 21.) In this article Mr. Wharam examines the possible defences that might be available to members of the Royal Navy if they were prosecuted for causing loss of life or damage to property in pursuance of the blockade. His conclusion is that no defence recognized by English law would be available, but the Crown would presumably not prosecute, and if a private prosecution were instituted one may suppose that the Attorney-General would issue a nolle prosequi. A foreign country whose subjects were the victims might or might not demand extradition, in which event the Crown would no doubt refuse to surrender its servants on the ground that the alleged crime ras of a political nature. On 6th April 1966, the Security Council of the United Nations called upon the Government of the United Kingdom to blockade Beira and if necessary to use force against any ship believed to be carrying oil to Rhodesia: the relevant part of the resolution reads as follows: “The Security Council calls upon the Government of the United Kingdom ... to prevent, by the use of force if necessary, the arrival at Beira of vessels reasonably believed to be carrying oil destined for Southern Rhodesia.

Parallel Quantum-Point-Contacts as High-Frequency-Mixers

We present the results of high-frequency mixing experiments performed upon parallel quantum point-contacts defined in the two-dimensional electron gas of an Al_{x}Ga_{1-x}As/GaAs-heterostructure. The parallel geometry, fabricated using a novel double-resist technology, enables the point-contact device to be impedance matched over a wide frequency range and, in addition, increases the power levels of the mixing signal while simultaneously reducing the parasitic source-drain capacitance. Here, we consider two parallel quantum point-contact devices with 155 and 110 point-contacts respectively; both devices operated successfully at liquid helium and liquid nitrogen temperatures with a minimal conversion loss of 13 dB.Comment: 4 figures, RevTeX, to be published in the 16 June 1997 issue of Applied Physic Letter

Ethical considerations in an era of mass drug administration

In a Plenary debate at the 51st Spring meeting of the British Society of Parasitology, Bristol, UK, April 8–11, 2013, the bioethicist James Wilson used the value of a life in the present and future to question the effectiveness of current health strategies

Mesoscopic Capacitance Oscillations

We examine oscillations as a function of Fermi energy in the capacitance of a mesoscopic cavity connected via a single quantum channel to a metallic contact and capacitively coupled to a back gate. The oscillations depend on the distribution of single levels in the cavity, the interaction strength and the transmission probability through the quantum channel. We use a Hartree-Fock approach to exclude self-interaction. The sample specific capacitance oscillations are in marked contrast to the charge relaxation resistance, which together with the capacitance defines the RC-time, and which for spin polarized electrons is quantized at half a resistance quantum. Both the capacitance oscillations and the quantized charge relaxation resistance are seen in a strikingly clear manner in a recent experiment.Comment: 9 pages, 2 figure

Microelectromagnets for Trapping and Manipulating Ultracold Atomic Quantum Gases

We describe the production and characterization of microelectromagnets made for trapping and manipulating atomic ensembles. The devices consist of 7 fabricated parallel copper conductors 3 micrometer thick, 25mm long, with widths ranging from 3 to 30 micrometer, and are produced by electroplating a sapphire substrate. Maximum current densities in the wires up to 6.5 * 10^6 A / cm^2 are achieved in continuous mode operation. The device operates successfully at a base pressure of 10^-11 mbar. The microstructures permit the realization of a variety of magnetic field configurations, and hence provide enormous flexibility for controlling the motion and the shape of Bose-Einstein condensates.Comment: 4 pages, 3 figure

Mechanism of electron localization in a quantum wire

We show that quasi-bound electron states are formed in a quantum wire as a result of electron backscattering in the transition regions between the wire and the electron reservoirs, to which the wire is coupled. The backscattering mechanism is caused by electron density oscillations arising even in smooth transitions due to the reflection of electrons not transmitting through the wire. The quasi-bound states reveal themselves in resonances of the electron transmission probability through the wire. The calculations were carried out within the Hartree-Fock approximation using quasiclassic wavefunctions.Comment: 7 pages, IOP style, 4 figures, typos corrected, published versio

On the Magnetic Nature of Quantum Point Contacts

We present results for a model that describes a quantum point contact. We show how electron-electron correlations, within the unrestricted Hartree-Fock approximation, generate a magnetic moment in the point contact. Having characterized the magnetic structure of the contact, we map the problem onto a simple one-channel model and calculate the temperature dependence of the conductance for different gate voltages. Our results are in good agreement with experimental results obtained in GaAs devices and support the idea of Kondo effect in these systems.Comment: 7 pages, 4 figure

Evidence of spontaneous spin polarized transport in magnetic nanowires

The exploitation of the spin in charge-based systems is opening revolutionary opportunities for device architecture. Surprisingly, room temperature electrical transport through magnetic nanowires is still an unresolved issue. Here, we show that ferromagnetic (Co) suspended atom chains spontaneously display an electron transport of half a conductance quantum, as expected for a fully polarized conduction channel. Similar behavior has been observed for Pd (a quasi-magnetic 4d metal) and Pt (a non-magnetic 5d metal). These results suggest that the nanowire low dimensionality reinforces or induces magnetic behavior, lifting off spin degeneracy even at room temperature and zero external magnetic field.Comment: 4 pages, 3 eps fig