51 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
Detecting chirality in two-terminal electronic devices
Central to spintronics is the interconversion between electronic charge and
spin currents, and this can arise from the chirality-induced spin selectivity
(CISS) effect. CISS is often studied as magnetoresistance (MR) in two-terminal
(2T) electronic devices containing a chiral (molecular) component and a
ferromagnet. However, fundamental understanding of when and how this MR can
occur is lacking. Here, we uncover an elementary mechanism that generates such
a MR for nonlinear response. It requires energy-dependent transport and energy
relaxation within the device. The sign of the MR depends on chirality, charge
carrier type, and bias direction. Additionally, we reveal how CISS can be
detected in the linear response regime in magnet-free 2T devices, either by
forming a chirality-based spin-valve using two or more chiral components, or by
Hanle spin precession in devices with a single chiral component. Our results
provide operation principles and design guidelines for chirality-based
spintronic devices and technologies
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
Detecting chirality in two-terminal electronic devices
Central to spintronics is the interconversion between electronic charge and
spin currents, and this can arise from the chirality-induced spin selectivity
(CISS) effect. CISS is often studied as magnetoresistance (MR) in two-terminal
(2T) electronic devices containing a chiral (molecular) component and a
ferromagnet. However, fundamental understanding of when and how this MR can
occur is lacking. Here, we uncover an elementary mechanism that generates such
a MR for nonlinear response. It requires energy-dependent transport and energy
relaxation within the device. The sign of the MR depends on chirality, charge
carrier type, and bias direction. Additionally, we reveal how CISS can be
detected in the linear response regime in magnet-free 2T devices, either by
forming a chirality-based spin-valve using two or more chiral components, or by
Hanle spin precession in devices with a single chiral component. Our results
provide operation principles and design guidelines for chirality-based
spintronic devices and technologies
Reply to "Comment on 'Spin-dependent electron transmission model for chiral molecules in mesoscopic devices'"
Here we emphasize once more the distinction between generating CISS
(spin-charge current conversion) in a chiral system and detecting it as
magnetoresistance in two-terminal electronic devices. We also highlight
important differences between electrical measurement results obtained in the
linear response regime and those obtained in the nonlinear regime
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