581 research outputs found
Detection of spin polarization with a side coupled quantum dot
We propose realistic methods to detect local spin polarization, which utilize
a quantum dot side coupled to the target system. By choosing appropriate states
in the dot, we can put spin selectivity to the dot and detect spins in the
target with small disturbance. We also present an experiment which realizes one
of the proposed spin detection schemes in magnetic fields.Comment: 5 pages, 6 figure
Spin filtering by a periodic nanospintronic devices
For a linear chain of diamond-like elements, we show that the Rashba
spin-orbit interaction (which can be tuned by a perpendicular gate voltage) and
the Aharonov-Bohm flux (due to a perpendicular magnetic field) can combine to
select only one propagating ballistic mode, for which the electronic spins are
fully polarized along a direction that can be tuned by the electric and
magnetic fields and by the electron energy. All the other modes are evanescent.
For a wide range of parameters, this chain can serve as a spin filter.Comment: Published versio
Topological classification of vortex-core structures of spin-1 Bose-Einstein condensates
We classify vortex-core structures according to the topology of the order
parameter space. By developing a method to characterize how the order parameter
changes inside the vortex core. We apply this method to the spin-1
Bose-Einstein condensates and show that the vortex-core structures are
classified by winding numbers that are locally defined in the core region. We
also show that a vortex-core structure with a nontrivial winding number can be
stabilized under a negative quadratic Zeeman effect.Comment: 16 pages, 6 figure
Filtering and analyzing mobile qubit information via Rashba-Dresselhaus-Aharonov-Bohm interferometers
Spin-1/2 electrons are scattered through one or two diamond-like loops, made
of quantum dots connected by one-dimensional wires, and subject to both an
Aharonov-Bohm flux and (Rashba and Dresselhaus) spin-orbit interactions. With
some symmetry between the two branches of each diamond, and with appropriate
tuning of the electric and magnetic fields (or of the diamond shapes) this
device completely blocks electrons with one polarization, and allows only
electrons with the opposite polarization to be transmitted. The directions of
these polarizations are tunable by these fields, and do not depend on the
energy of the scattered electrons. For each range of fields one can tune the
site and bond energies of the device so that the transmission of the fully
polarized electrons is close to unity. Thus, these devices perform as ideal
spin filters, and these electrons can be viewed as mobile qubits; the device
writes definite quantum information on the spinors of the outgoing electrons.
The device can also read the information written on incoming polarized
electrons: the charge transmission through the device contains full information
on this polarization. The double-diamond device can also act as a realization
of the Datta-Das spin field-effect transistor.Comment: 13 pages, 8 figure
Anomalous In-Plane Anisotropy of the Onset of Superconductivity in (TMTSF)2ClO4
We report the magnetic field-amplitude and field-angle dependence of the
superconducting onset temperature Tc_onset of the organic superconductor
(TMTSF)2ClO4 in magnetic fields H accurately aligned to the conductive ab'
plane. We revealed that the rapid increase of the onset fields at low
temperatures occurs both for H // b' and H // a, irrespective of the carrier
confinement. Moreover, in the vicinity of the Pauli limiting field, we report a
shift of a principal axis of the in-plane field-angle dependence of Tc_onset
away from the b' axis. This feature may be related to an occurrence of
Fulde-Ferrell-Larkin-Ovchinnikov phases.Comment: 4 pages, 4 figure
Nearly free electrons in the layered oxide superconductor Ag5Pb2O6
We present first measurements of quantum oscillations in the layered oxide
superconductor
Ag5Pb2O6. From a detailed angular and temperature dependent study of the dHvA
effect we determine the electronic structure and demonstrate that the electron
masses are very light, m^* is approximately equalt to 1.2 m_e. The Fermi
surface we observe is essentially that expected of nearly-free electrons -
establishing
Ag5Pb2O6 as the first known example of a monovalent, nearly-free electron
superconductor at ambient pressure.Comment: 4 pages, 3 figure
Chaos in Static Axisymmetric Spacetimes I : Vacuum Case
We study the motion of test particle in static axisymmetric vacuum spacetimes
and discuss two criteria for strong chaos to occur: (1) a local instability
measured by the Weyl curvature, and (2) a tangle of a homoclinic orbit, which
is closely related to an unstable periodic orbit in general relativity. We
analyze several static axisymmetric spacetimes and find that the first
criterion is a sufficient condition for chaos, at least qualitatively. Although
some test particles which do not satisfy the first criterion show chaotic
behavior in some spacetimes, these can be accounted for the second criterion.Comment: More comments for the quantitative estimation of chaos are added, and
some inappropriate terms are changed. This will appear on Class. Quant. Gra
Innermost Stable Circular Orbit of a Spinning Particle in Kerr Spacetime
We study stability of a circular orbit of a spinning test particle in a Kerr
spacetime. We find that some of the circular orbits become unstable in the
direction perpendicular to the equatorial plane, although the orbits are still
stable in the radial direction. Then for the large spin case ($S < \sim O(1)),
the innermost stable circular orbit (ISCO) appears before the minimum of the
effective potential in the equatorial plane disappears. This changes the radius
of ISCO and then the frequency of the last circular orbit.Comment: 25 pages including 8 figure
Designing isolation guidelines for COVID-19 patients with rapid antigen tests
新型コロナウイルス感染者の隔離短縮は可能か?. 京都大学プレスリリース. 2022-08-24.Appropriate isolation guidelines for COVID-19 patients are warranted. Currently, isolating for fixed time is adopted in most countries. However, given the variability in viral dynamics between patients, some patients may no longer be infectious by the end of isolation, whereas others may still be infectious. Utilizing viral test results to determine isolation length would minimize both the risk of prematurely ending isolation of infectious patients and the unnecessary individual burden of redundant isolation of noninfectious patients. In this study, we develop a data-driven computational framework to compute the population-level risk and the burden of different isolation guidelines with rapid antigen tests (i.e., lateral flow tests). Here, we show that when the detection limit is higher than the infectiousness threshold values, additional consecutive negative results are needed to ascertain infectiousness status. Further, rapid antigen tests should be designed to have lower detection limits than infectiousness threshold values to minimize the length of prolonged isolation
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