SEARCH · Search NASA
Results for “spin selectivity”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Inducing Chiral Photoluminescence in Single Photon Quantum Emitters using Chiral Induced Spin Selectivity
Explore the source record for details and available documents.
Combined Coherent Manipulation and Single-Shot Measurement of an Electron Spin in a Quantum Dot (Final Technical Report)
Semiconductor quantum dots (QDs) are promising candidates to act as single-photon sources and/or quantum bits in future optical quantum information applications. Their excellent optical properties such as high brightness, single-photon purity, and narrow linewidth have potential utility in many areas. One challenge is to control the energy levels of the QD without using a magnetic field. The AC Stark effect offers the opportunity to do this. We have demonstrated record-large AC Stark shifts of the energy states of a single charged QD. We showed that the shifts can be applied in a spin-selective manner by controlling the polarization of the laser producing the AC Stark effect. In order to characterize the effect, we developed a novel spectral filtering scheme to discriminate the high-power AC Stark laser from the QD fluorescence. We also developed a compact, low-cost, homemade polarimeter to help control the polarization of the AC Stark laser, which enabled the spin selectivity of the AC Stark effect. With the practical capabilities thus developed, we learned that the spin-selective AC Stark effect causes electron spin pumping, which in turn causes nuclear spin pumping via the hyperfine interaction. The nuclear spin pumping causes a mean field Zeeman interaction between the nuclear spin ensemble and the electron trapped in the QD, resulting in the so-called Overhauser shift. The magnitude of the Overhauser shift and the measured linewidth of the QD’s optical transitions enabled characterization of the mean nuclear spin polarization and fluctuations. The potentially rapid (ns-scale) control of the QD energy levels and nuclear spin polarization will enable measurements of electron and nuclear spin polarization in the absence of any real magnetic field, which is a completely unique capability. The ability to rapidly apply a spin-selective AC Stark effect in the presence of a weak real magnetic field will allow control of the polarization selection rules of the transitions, enabling all single-qubit operations on the electron spin, i.e., initialization, coherent manipulation, and quantum non-demolition measurement.
Recent advancements in chiral spintronics: from molecular-level insights to device applications. A prospect based on the interplay between physical and chemical properties of chiral systems
This review discusses recent advancements in chiral-based spin-electronic devices achieved using suitable combinations of organic, inorganic and hybrid materials. The focus is on how chirality can be effectively used to control spin in practical applications, particularly in spintronic sensors and consumer devices. Interestingly, the underlying mechanism for this control is the chiral-induced spin selectivity (CISS) effect, which links the structural chirality of a material to its spin-selective electronic transport properties. The CISS effect arises from the observation that charge transmission in chiral systems is spin selective. Experimental evidence suggests a relationship between electron spin and the structural handedness of the material. In conclusion, this unique structure-transport relationship can be exploited to design a wide range of spintronics devices, including memory, transistors, logic gates and molecular q-bits.
Spin polarization through axially chiral linkers: Length dependence and correlation with the dissymmetry factor
Abstract The chiral‐induced spin selectivity (CISS) effect relates to the spin‐selective electron transport through chiral molecules; therefore, the chiral molecules act as spin filters. In past studies, correlation was found between the magnitude of the spin filtering and the intensity of the circular dichroism (CD) spectrum (the first Compton peak) of the molecules. Since the intensity of the CD peak relates to both the magnitude of the electric and magnetic dipole transitions, it was not clear which of these properties correlate with the CISS effect. This work aims at addressing this question. By studying the spin‐dependent conduction and the CD spectra of the thiol‐functionalized enantiopure binaphthalene (BINAP) and ternaphthalene (TERNAP), we found that both BINAP and TERNAP exhibit a similar spin polarization of 50%, despite the first Compton peak in TERNAP being almost twice as intense as the peak in BINAP. These results can be explained by the similar values of their anisotropy (or dissymmetry) factor, g abs , which is proportional to the magnetic transition dipole moment. Hence, we concluded that the CISS effect is proportional to the transition dipole moment in chiral molecules, namely, to the dissymmetry factor.
Adsorption-Induced Surface Magnetism
We report the emergence of adsorption-induced magnetism from heterohelicene molecules on a nonmagnetic Cu(100) surface. Spin-polarized low-energy electron microscopy measurements reveal spin-dependent electron reflectivity for enantiopure 7,12,17-trioxa[11]helicene (TO[11]H) monolayers, indicating the formation of a spin-polarized state localized in the topmost copper layer. Control experiments on clean Cu(100) and TO[11]H on highly oriented pyrolytic graphite show no such effect, excluding artifacts and chirality-induced spin selectivity as origins. Spin-polarized density functional theory calculations with hybrid functionals attribute the magnetism to strong chemisorption, which induces hybridization between the molecular HOMO and copper s- and d-states, driving asymmetric spin-polarized charge redistribution at the interface. An extended Newns-Anderson-Grimley model incorporating on-site Coulomb repulsion in Cu d-orbitals reproduces the emergence of interfacial spin polarization above a threshold interaction strength, highlighting the key roles of hybridization parameters and Coulomb correlation. These findings reveal a mechanism for inducing magnetism at molecule-metal interfaces without inherently magnetic components, offering avenues for engineering spin-polarized states in organic-inorganic hybrid systems.
Unconventional Spintronics from Chiral Perovskites
Spintronic devices typically employ heterostructures with ferromagnets which break time-reversal symmetry and have non-vanishing magnetization. With the growing class of materials that support spin-polarized carriers, current, and excitations, it is possible to envision emerging spintronic applications that are not limited to magnetoresistance. Here, chiral perovskites with no net magnetization are considered, where the space-inversion and mirror symmetries are broken to induce chiral structure. The known importance of these perovskites is further expanded by the demonstration of the chiral-induced spin selectivity (CISS). However, the generation of the spin-polarized carriers across the interface with these chiral perovskites remains to be fully understood. These first-principles studies for 2D PbBr4-based chiral perovskites provide their electronic structure and an orbital-based symmetry analysis, which allows to establish an effective Hamiltonian to elucidate the underlying origin of their chirality. The same analysis is used for the Edelstein effect, responsible for electrical generation of the nonequilibrium spin polarization in many materials, which in chiral perovskites can be a mechanism contributing to CISS. Furthermore, by examining optical properties of chiral perovskites and the opportunity to use them to realize tunable altermagnets, another class of zero-magnetization spintronic materials, a versatile materials platform is put forth for unconventional spintronics.
Growth Dynamics and Electron Reflectivity in Ultrathin Films of Chiral Heptahelicene on Metal (100) Surfaces Studied by Spin-Polarized Low Energy Electron Microscopy
Interaction of electrons with chiral matter gives rise to interesting phenomena such as the chirality-induced spin selectivity. The interdependence of reflectivity of spin-polarized low energy electrons and the absolute handedness of chiral molecules is investigated. First, the growth of homochiral films of helical aromatic hydrocarbons, so-called helicenes, on a Cu(100) surface is studied by means of low energy electron microscopy and scanning tunneling microscopy in ultrahigh vacuum. As soon as the coverage exceeds one monolayer, double-layer nucleation and growth is favored such that depletion in the first layer occurs. Spatially resolved work function measurements show that second-layer patches have a lower work function than first-layer areas. Reflectivity spectra of spin-polarized electrons do not show any asymmetry between homochiral films of the enantiomers. Laterally resolved work function measurements do not confirm work function differences such as those reported earlier for photoelectron studies of chiral peptide films on ferromagnetic substrates.
Chirality enhances oxygen reduction
Controlled reduction of oxygen is important for developing clean energy technologies, such as fuel cells, and is vital to the existence of aerobic organisms. The process starts with oxygen in a triplet ground state and ends with products that are all in singlet states. Hence, spin constraints in the oxygen reduction must be considered. Here, we show that the electron transfer efficiency from chiral electrodes to oxygen (oxygen reduction reaction) is enhanced over that from achiral electrodes. We demonstrate lower overpotentials and higher current densities for chiral catalysts versus achiral ones. This finding holds even for electrodes composed of heavy metals with large spin–orbit coupling. The effect results from the spin selectivity conferred on the electron current by the chiral assemblies, the chiral-induced spin selectivity effect.
Spin-dependent electron transfer in electrochemically transparent van der Waals heterostructures for oxygen evolution reaction
Spin selective catalysis is an emerging approach for improving the thermodynamics and kinetics of reactions. The role of electron spins has been scarcely studied in catalytic reactions. One exception is the oxygen evolution reaction (OER) where strongly correlated metals and oxides are used as catalysts. In OER, spin alignment facilitates the transition of singlet state of the reactant to the triplet state of O 2 . However, the influence of strong correlations on spin exchange mechanism and spin selective thermodynamics of most catalytic reactions remain unclear. Here we decouple the strongly correlated catalyst from the electrolyte to study spin exchange in two-dimensional (2D) magnetic iron germanium telluride (FGT) heterostructure. We demonstrate that transmission of spin and electrochemical information between the catalyst and the reactant can occur through quantum exchange interaction despite the catalyst of FGT being completely encapsulated by graphene or hexagonal boron nitride (hBN). The strong correlations in FGT that lead to enhanced spin exchange in OER are observed in graphene or hBN layers with thicknesses of up to 6 nm. We demonstrate that spin alignment in FGT leads to a lowering of thermodynamic barrier for adsorption of hydroxide ion and electron transfer to the catalyst. This results in up to fivefold enhancement in OER performance and improved kinetics. Our results provide clear evidence that transmission of both quantum mechanical and electrochemical information through quantum spin exchange interaction in FGT leads to an enhancement in catalytic performance.
On triality defects in 2d CFT
We consider the triality fusion category discovered in the c = 1 Kosterlitz-Thouless theory. We analyze this fusion category using the tools from the group theoretical fusion category and compute the simple lines, fusion rules and F-symbols. We then studied the physical implication of this fusion category including deriving the spin selection rule, computing the asymptotic density of states of irreducible representations of the fusion category symmetries, and analyzing its anomaly and constraints under the renormalization group flow. There is another set of F-symbols for the fusion categories with the same fusion rule known in the literature. We find these two solutions are different as they lead to different spin selection rules. This gives a complete list of the fusion categories with the same fusion rule by the classification result in.
Interplay between Chiro-Optical and Spin Transport Properties in Chiral CdSe Quantum Dots
The chiral-induced spin selectivity (CISS) effect offers compelling approaches for manipulating spin-dependent processes in both chemistry and physics, yet the physical mechanism(s) underpinning CISS are still debated. Here we present a study of structure-property relationships in chiral quantum dot assemblies to identify attributes of CISS-based phenomena. Our results show that the circular dichroism (CD) strength of chiral CdSe quantum dots’ primary exciton transition correlates with two CISS properties, the propensity to transmit pure spin currents and to produce spin-polarized charge currents. While the spin-polarized charge current reverses its sign with a change in the polarity of the CD signal, the pure spin current transport does not. The trends in both transport types can be rationalized in terms of chirality-induced splitting of spin sub-bands, which are modulated by chiral symmetry breaking under charge transport through the CdSe quantum dots.
Vibronic Coupling and Exciton Chirality: Electronic and Structural Rearrangement between Helical to Zero Momentum Molecular Exciton States
Helical porphyrin aggregates are attractive macromolecular nanostructures for biomimetic light-harvesting and energy transfer in solar energy technology due to their large light absorbing cross sections and promising energy conservation benefits from chiral-induced spin selectivity. However, with these soft materials, it is imperative that we understand how the nuclear degrees of freedom impact the excitonic energy landscape and dynamics, particularly pertaining to how it influences the chiral angular momentum of the excitons. To this end, we have measured time-resolved depolarization ratios using femtosecond stimulated Raman spectroscopy to uncover the vibronic coupling guided by molecular vibrations between excitons of different angular momentum in helical tetra(sulfonatophenyl)porphyrin aggregates. We find that while transient absorption anisotropy reveals rapid (1 ps lifetime) exciton rotation from helical to achiral states in the Q-band, time-resolved vibrational depolarization ratios evolve on remarkably faster time scales (<500 fs lifetime) for the totally symmetric 1530 cm –1 vibration and the nontotally symmetric 1540 cm –1 vibration. The time-resolved depolarization ratios of the 1540 cm –1 vibration, in particular, show strong evidence of vibronic coupling and nonadiabatic exciton behavior that mediates the nonradiative transition between chiral and achiral excitons. Furthermore, our study shows that for rational design of helical molecular aggregates for exciton transport, the vibronic coupling between excitons of different angular momenta driven by molecular vibrations must be considered especially in the case where chiral-induced spin selectivity is desired.
Structural descriptor for enhanced spin-splitting in 2D hybrid perovskites
Abstract Two-dimensional (2D) hybrid metal halide perovskites have emerged as outstanding optoelectronic materials and are potential hosts of Rashba/Dresselhaus spin-splitting for spin-selective transport and spin-orbitronics. However, a quantitative microscopic understanding of what controls the spin-splitting magnitude is generally lacking. Through crystallographic and first-principles studies on a broad array of chiral and achiral 2D perovskites, we demonstrate that a specific bond angle disparity connected with asymmetric tilting distortions of the metal halide octahedra breaks local inversion symmetry and strongly correlates with computed spin-splitting. This distortion metric can serve as a crystallographic descriptor for rapid discovery of potential candidate materials with strong spin-splitting. Our work establishes that, rather than the global space group, local inorganic layer distortions induced via appropriate organic cations provide a key design objective to achieve strong spin-splitting in perovskites. New chiral perovskites reported here couple a sizeable spin-splitting with chiral degrees of freedom and offer a unique paradigm of potential interest for spintronics.
Band-Selective Spin-Charge Separation across the Charge Density Wave Transition in Quasi-1D NbSe 3
Non-Fermi liquid (non-FL) phase is a pivotal enigma in understanding intriguing quantum phases in strongly correlated systems, such as high-temperature superconductivity. Tomonaga-Luttinger liquid (TLL) theory, designed for one-dimensional (1D) systems, serves as one of the microscopic frameworks that elucidates non-FL behavior. Despite its theoretical concreteness, comprehensive experimental verification has remained incomplete. In particular, addressing the persistence of the TLL nature within ordered phases, such as charge density wave (CDW), has posed a significant challenge. We report the observation of TLL characteristics across the CDW transitions in a quasi-1D material NbSe 3 using angle-resolved photoemission spectroscopy. Spin-charge separation, a disentanglement of spin and charge degrees of freedom of electrons, is clearly observed within the band, accompanied by the suppression of spectral weight following a power-law behavior with anticipated temperature scaling. Surprisingly, the spin-charge separation persists even below the CDW transition temperatures, indicating the validity of the TLL nature in the CDW phase. In conclusion, our findings offer a unique opportunity to explore the interplay between the TLL and ordered phases, which could be connected to the interplay between non-FL and ordered phases in strongly correlated systems.
Equilibrium spin polarization arising from chirality
Chirality-induced spin selectivity (CISS) describes how chiral molecules and materials generate spin polarization even at thermal equilibrium. This observation has challenged established principles of microscopic reversibility and Onsager reciprocity. We resolve this paradox by formulating a pseudo-Hermitian quantum framework that separates thermodynamic equilibrium from time-reversal symmetry. Within this approach, structural chirality and electron correlations, irrespective of their microscopic origin, are sufficient to produce CISS observables. Chirality enters through a non-local metric η that couples spin and spatial motion, leading to real spectra, unitary evolution, and thermodynamic consistency. The framework predicts a chirality-induced spin magnetic ordering characterized by a spin-displacement order, which reconciles equilibrium spin polarization with detailed balance and explains the persistence of CISS in materials composed of light elements. We derive generalized Onsager-Casimir relations that respect the observed CISS symmetry, i.e., parity $(\mathscr{P})$-odd and time-reversal $(\mathscr{T})$-odd, but exhibiting $\mathscr{PT}$-even symmetry. This approach establishes a coherent foundation for equilibrium CISS and provides a route to link chemical chirality with measurable spin-to-charge conversion effects.
Spin-Polarized Oxygen Evolution Reaction Enabled by Chiral Molecules Coupled with Ferromagnetic Electrocatalysts
The discovery of chirality-induced spin selectivity (CISS) revolutionized our understanding of the capabilities of chiral molecules, revealing that chiral molecules can function as spin filters, aligning the spin orientation of electrons when they transmit through them. Recently, CISS has been exploited to direct energy conversion, especially the oxygen evolution reaction (OER). However, despite the remarkable progress that has been achieved, the effect of CISS in influencing the intermediate species formation and changing the rate-determining step (RDS) is still vague. To understand those key reaction mechanism steps, electrocatalysts with distinct magnetic characteristics, ferromagnetic CoFe2O4 and paramagnetic Co3O4, were synthesized. The results show that spin-polarized charge carriers retain their spin alignment when coupled with ferromagnetic CoFe2O4, akin to the behavior observed under a magnetic field. The Tafel analysis and kinetic isotope studies (kinetic isotope effect) suggest that in the absence of chiral molecules, the initial electron transfer step, the formation of O* species, governs the rate-determining step (RDS). However, introducing chiral molecules shifts the RDS to a combination of the first and second electron transfers, leading to the formation of OOH*. This conclusion was further supported by in situ infrared spectroscopy, which shows that l-methionine-modified CoFe2O4 (l-CoFe2O4) promotes the formation of OOH*, a key intermediate for O2 generation. This study highlights the critical role of CISS in affecting the OER mechanism and intermediate species formation.