1,648 research outputs found
Coherent resistance of a disordered 1D wire: Expressions for all moments and evidence for non-Gaussian distribution
We study coherent electron transport in a one-dimensional wire with disorder
modeled as a chain of randomly positioned scatterers. We derive analytical
expressions for all statistical moments of the wire resistance . By means
of these expressions we show analytically that the distribution of the
variable is not exactly Gaussian even in the limit of weak
disorder. In a strict mathematical sense, this conclusion is found to hold not
only for the distribution tails but also for the bulk of the distribution
.Comment: Revised version, 8 pages, 4 figures, RevTeX
Spin-engineered quantum dots
Spatially nonhomogeneously spin polarized nuclei are proposed as a new
mechanism to monitor electron states in a nanostructure, or as a means to
createn and, if necessary, reshape such nanostructures in the course of the
experiment. We found that a polarization of nulear spins may lift the spin
polarization of the electron states in a nanostructure and, if sufficiently
strong, leads to a polarization of the electron spins. Polarized nuclear spins
may form an energy landscape capable of binding electrons with energy up to
several meV and the localization radius 100\AA.Comment: 9 pages, 1 figure, submitted to Physica E, Augist 31, 200
Massive Spin Collective Mode in Quantum Hall Ferromagnet
It is shown that the collective spin rotation of a single Skyrmion in quantum
Hall ferromagnet can be regarded as precession of the entire spin texture in
the external magnetic field, with an effective moment of inertia which becomes
infinite in the zero g-factor limit. This low-lying spin excitation may
dramatically enhance the nuclear spin relaxation rate via the hyperfine
interaction in the quantum well slightly away from filling factor equal one.Comment: 4 page
Stranger in a Strange Land: Old Chair, New University
There are opportunities and challenges associated with appointing a chair from within and from outside the organization. This discussion will consider multiple aspects and focus on considerations for changing institutions to assume the chair position
Nucleus-mediated spin-flip transitions in GaAs quantum dots
Spin-flip rates in GaAs quantum dots can be quite slow, thus opening up the
possibilities to manipulate spin states in the dots. We present here
estimations of inelastic spin-flip rates mediated by hyperfine interaction with
nuclei. Under general assumptions the nucleus mediated rate is proportional to
the phonon relaxation rate for the corresponding non-spin-flip transitions. The
rate can be accelerated in the vicinity of a singlet-triplet excited states
crossing. The small proportionality coefficient depends inversely on the number
of nuclei in the quantum dot. We compare our results with known mechanisms of
spin-flip in quantum dot.Comment: RevTex 4 pages, 1 figure, submitted to Phys. Rev.
Resolution of Conflicting Signals at the Single-Cell Level in the Regulation of Cyanobacterial Photosynthesis and Nitrogen Fixation
Unicellular, diazotrophic cyanobacteria temporally separate dinitrogen (N-2) fixation and photosynthesis to prevent inactivation of the nitrogenase by oxygen. This temporal segregation is regulated by a circadian clock with oscillating activities of N-2 fixation in the dark and photosynthesis in the light. On the population level, this separation is not always complete, since the two processes can overlap during transitions from dark to light. How do single cells avoid inactivation of nitrogenase during these periods? One possibility is that phenotypic heterogeneity in populations leads to segregation of the two processes. Here, we measured N-2 fixation and photosynthesis of individual cells using nanometer-scale secondary ion mass spectrometry (nanoSIMS) to assess both processes in a culture of the unicellular, diazotrophic cyanobacterium Crocosphaera watsonii during a dark-light and a continuous light phase. We compared single-cell rates with bulk rates and gene expression profiles. During the regular dark and light phases, C. watsonii exhibited the temporal segregation of N-2 fixation and photosynthesis commonly observed. However, N-2 fixation and photosynthesis were concurrently measurable at the population level during the subjective dark phase in which cells were kept in the light rather than returned to the expected dark phase. At the single-cell level, though, cells discriminated against either one of the two processes. Cells that showed high levels of photosynthesis had low nitrogen fixing activities, and vice versa. These results suggest that, under ambiguous environmental signals, single cells discriminate against either photosynthesis or nitrogen fixation, and thereby might reduce costs associated with running incompatible processes in the same cell
Nuclear-spin qubits interaction in mesoscopic wires and rings
Theoretical study of the indirect coupling of nuclear spins (qubits) embedded
into a mesoscopic ring and in a finite length quantum wire in a magnetic field
is presented. It is found that the hyperfine interaction, via the conduction
electrons, between nuclear spins exhibits sharp maxima as function of the
magnetic field and nuclear spin positions. This phenomenon can be used for
manipulation of qubits with almost atomic precision. Experimental feasibility
and implications for quantum logics devices is discussed.Comment: 3 figures, 12 page
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