1,729 research outputs found
Spin-Dependent Electron Transmission Model for Chiral Molecules in Mesoscopic Devices
Various device-based experiments have indicated that electron transfer in
certain chiral molecules may be spin-dependent, a phenomenon known as the
Chiral Induced Spin Selectivity (CISS) effect. However, due to the complexity
of these devices and a lack of theoretical understanding, it is not always
clear to what extent the chiral character of the molecules actually contributes
to the magnetic-field-dependent signals in these experiments. To address this
issue, we report here an electron transmission model that evaluates the role of
the CISS effect in two-terminal and multi-terminal linear-regime electron
transport experiments. Our model reveals that for the CISS effect, the
chirality-dependent spin transmission is accompanied by a spin-flip electron
reflection process. Furthermore, we show that more than two terminals are
required in order to probe the CISS effect in the linear regime. In addition,
we propose two types of multi-terminal nonlocal transport measurements that can
distinguish the CISS effect from other magnetic-field-dependent signals. Our
model provides an effective tool to review and design CISS-related transport
experiments, and to enlighten the mechanism of the CISS effect itself
Circuit-Model Analysis for Spintronic Devices with Chiral Molecules as Spin Injectors
Recent research discovered that charge transfer processes in chiral molecules
can be spin selective and named the effect chiral-induced spin selectivity
(CISS). Follow-up work studied hybrid spintronic devices with conventional
electronic materials and chiral (bio)molecules. However, a theoretical
foundation for the CISS effect is still in development and the spintronic
signals were not evaluated quantitatively. We present a circuit-model approach
that can provide quantitative evaluations. Our analysis assumes the scheme of a
recent experiment that used photosystem~I (PSI) as spin injectors, for which we
find that the experimentally observed signals are, under any reasonable
assumptions on relevant PSI time scales, too high to be fully due to the CISS
effect. We also show that the CISS effect can in principle be detected using
the same type of solid-state device, and by replacing silver with graphene, the
signals due to spin generation can be enlarged four orders of magnitude. Our
approach thus provides a generic framework for analyzing this type of
experiments and advancing the understanding of the CISS effect
All-optical coherent population trapping with defect spin ensembles in silicon carbide
Divacancy defects in silicon carbide have long-lived electronic spin states
and sharp optical transitions, with properties that are similar to the
nitrogen-vacancy defect in diamond. We report experiments on 4H-SiC that
investigate all-optical addressing of spin states with the zero-phonon-line
transitions. Our magneto-spectroscopy results identify the spin structure
of the ground and excited state, and a role for decay via intersystem crossing.
We use these results for demonstrating coherent population trapping of spin
states with divacancy ensembles that have particular orientations in the SiC
crystal.Comment: 28 page document: Pages 1-14 main text (with 3 figures); pages 15-28
supplementary information (with 5 figues). v2 has minor correction
Soft modes near the buckling transition of icosahedral shells
Icosahedral shells undergo a buckling transition as the ratio of Young's
modulus to bending stiffness increases. Strong bending stiffness favors smooth,
nearly spherical shapes, while weak bending stiffness leads to a sharply
faceted icosahedral shape. Based on the phonon spectrum of a simplified
mass-and-spring model of the shell, we interpret the transition from smooth to
faceted as a soft-mode transition. In contrast to the case of a disclinated
planar network where the transition is sharply defined, the mean curvature of
the sphere smooths the transitition. We define elastic susceptibilities as the
response to forces applied at vertices, edges and faces of an icosahedron. At
the soft-mode transition the vertex susceptibility is the largest, but as the
shell becomes more faceted the edge and face susceptibilities greatly exceed
the vertex susceptibility. Limiting behaviors of the susceptibilities are
analyzed and related to the ridge-scaling behavior of elastic sheets. Our
results apply to virus capsids, liposomes with crystalline order and other
shell-like structures with icosahedral symmetry.Comment: 28 pages, 6 figure
Capacitive coupling of atomic systems to mesoscopic conductors
We describe a technique that enables a strong, coherent coupling between
isolated neutral atoms and mesoscopic conductors. The coupling is achieved by
exciting atoms trapped above the surface of a superconducting transmission line
into Rydberg states with large electric dipole moments, that induce voltage
fluctuations in the transmission line. Using a mechanism analogous to cavity
quantum electrodynamics an atomic state can be transferred to a long-lived mode
of the fluctuating voltage, atoms separated by millimeters can be entangled, or
the quantum state of a solid state device can be mapped onto atomic or photonic
states.Comment: 4 pages, including one figure. v2: Improved discussion of surface
effect
Utility analysis of disability caused by amblyopia and/or strabismus in a population-based, historic cohort
Random regret minimization or random utility maximization: An exploratory analysis in the context of automobile fuel choice
Interest in alternative behavioural paradigms to random utility maximisation (RUM) has existed ever since the dominance of the RUM formulation. One alternative is known as random regret minimisation (RRM), which suggests that when choosing between alternatives, decision-makers aim to minimise anticipated regret. Although the idea of regret is not new, its incorporation into the same discrete choice framework of RUM is very recent. This paper is the first to apply the RRM-model framework to model choice among durable goods. Specifically, we estimate and compare RRM- and RUM-models in a stated choice context of choosing amongst petrol, diesel and hybrid fuelled vehicles (associated with specific levels of fuel efficiency and engine capacity). The RRM-model is found to achieve a marginally better fit (using a non-nested test of differences) than its equally parsimonious RUM-counterpart. As a second contribution, we derive a formulation for regret-based elasticities, and compare utility- and regret-based elasticities in the context of stated vehicle-type choices. We find that in the context of our choice-data, mean estimates of elasticities are different for many of the attributes and alternatives
Entanglement between charge qubits induced by a common dissipative environment
We study entanglement generation between two charge qubits due to the strong
coupling with a common bosonic environment (Ohmic bath). The coupling to the
boson bath is a source of both quantum noise (leading to decoherence) and an
indirect interaction between qubits. As a result, two effects compete as a
function of the coupling strength with the bath: entanglement generation and
charge localization induced by the bath. These two competing effects lead to a
non-monotonic behavior of the concurrence as a function of the coupling
strength with the bath. As an application, we present results for charge qubits
based on double quantum dots.Comment: 9 pages, 7 figure
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