A methodology for the design and evaluation of minerals extraction processes

Imperial Users onl

Sensitivity of the magnetic state of a spin lattice on itinerant electron orbital phase

Spatially extended localized spins can interact via indirect exchange interaction through Friedel oscillations in the Fermi sea. In arrays of localized spins such interaction can lead to a magnetically ordered phase. Without external magnetic field such a phase is well understood via a "two-impurity" Kondo model. Here we employ non-equilibrium transport spectroscopy to investigate the role of the orbital phase of conduction electrons on the magnetic state of a spin lattice. We show experimentally, that even tiniest perpendicular magnetic field can influence the magnitude of the inter-spin magnetic exchange.Comment: To be published in PhysicaE EP2DS proceedin

Fano effect and Kondo effect in quantum dots formed in strongly coupled quantum wells

We present lateral transport measurements on strongly, vertically coupled quantum dots formed in separate quantum wells in a GaAs/AlGaAs heterostructure. Coulomb oscillations are observed forming a honeycomb lattice consistent with two strongly coupled dots. When the tunnel barriers in the upper well are reduced we observe the Fano effect due to the interfering paths through a resonant state in the lower well and a continuum state in the upper well. In both regimes an in plane magnetic field reduces the coupling between the wells when the magnetic length is comparable to the center to center separation of the wells. We also observe the Kondo effect which allows the spin states of the double dot system to be probed.Comment: 4 pages, 5 figure

Designing prevention programmes to reduce incidence of dementia: prospective cohort study of modifiable risk factors

Objective To estimate the percentage reduction in incidence of dementia that would be obtained if specific risk factors were eliminated

Kondo Effect in a Quantum Antidot

We report Kondo-like behaviour in a quantum antidot (a submicron depleted region in a two-dimensional electron gas) in the quantum-Hall regime. When both spin branches of the lowest Landau level encircle the antidot in a magnetic field ($\sim 1$ T), extra resonances occur between extended edge states via antidot bound states when tunnelling is Coulomb blockaded. These resonances appear only in alternating Coulomb-blockaded regions, and become suppressed when the temperature or source-drain bias is raised. Although the exact mechanism is unknown, we believe that Kondo-like correlated tunnelling arises from skyrmion-type edge reconstruction. This observation demonstrates the generality of the Kondo phenomenon.Comment: 9 pages, 3 figures (Fig.3 in colour), to appear in Phys. Rev. Let

Suspended two-dimensional electron gases in In₀.₇₅Ga₀.₂₅As quantum wells

We demonstrate that In0.75Ga0.25As quantum wells can be freely suspended without losing electrical quality when the epitaxial strain-relieving buffer layer is removed. In applied magnetic fields, non-dissipative behavior is observed in the conductivity, and a current induced breakdown of the quantum Hall effect shows a lower critical current in the suspended layers due to efficient thermal isolation compared to the non-suspended-control device. Beyond the critical current, background impurity scattering in the suspended two-dimensional channel regions dominates with stochastic, resonant-like features in the conductivity. This device fabrication scheme offers the potential for thermally isolated devices containing suspension-asymmetry-induced, high spin–orbit coupling strengths with reduced electron–phonon interaction behavior but without introducing high levels of disorder in the processing. This work was funded by EPSRC Grant Nos. EP/K004077/1 and EP/R029075/1, UK. We thank Professor Chris Ford for useful discussions