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Yossi Paltiel

Publications and source records attributed to Yossi Paltiel.

32 records · Page 2Linked to original sources
arXiv2021

Theory of Chirality Induced Spin Selectivity: Progress and Challenges

We provide a critical overview of the theory of the chirality-induced spin selectivity (CISS) effect, i.e., phenomena in which the chirality of molecular species imparts significant spin selectivity to various electron processes. Based on discussions in a recently held workshop, and further work published since, we review the status of CISS effects - in electron transmission, electron transport, and chemical reactions. For each, we provide a detailed discussion of the state-of-the-art in theoretical understanding and identify remaining challenges and research opportunities.

cond-mat.mtrl-sci↗
arXiv2021

Interplay between friction and spin-orbit coupling as a source of spin polarization

We study an effective one-dimensional quantum model that includes friction and spin-orbit coupling (SOC), and show that the model exhibits spin polarization when both terms are finite. Most important, strong spin polarization can be observed even for moderate SOC, provided that friction is strong. Our findings might help to explain the pronounced effect of chirality on spin distribution and transport in chiral molecules. In particular, our model implies static magnetic properties of a chiral molecule, which lead to Shiba-like states when a molecule is placed on a superconductor, in accordance with recent experimental data.

cond-mat.mes-hall↗
arXiv2021

Role of Exchange Interactions in the Magnetic Response and Intermolecular Recognition of Chiral Molecules

The physical origin of the so-called chirality-induced spin selectivity (CISS) effect has puzzled experimental and theoretical researchers over the past few years. Early experiments were interpreted in terms of unconventional spin-orbit interactions mediated by the helical geometry. However, more recent experimental studies have clearly revealed that electronic exchange interactions also play a key role in the magnetic response of chiral molecules in singlet states. In this investigation, we use spin-polarized closed shell density functional theory calculations to address the influence of exchange contributions to the interaction between helical molecules as well as of helical molecules with magnetized substrates. We show that exchange effects result in differences in the interaction properties with magnetized surfaces, shedding light into the possible origin of two recent important experimental results: enantiomer separation and magnetic exchange force microscopy with AFM tips functionalized with helical peptides.

cond-mat.mes-hall↗
arXiv2021

Long-Timescale Magnetization Ordering Induced by an Adsorbed Chiral Monolayer on Ferromagnets

When an electron passes through a chiral molecule there is a high probability for a correlation between the momentum and spin of the charge, thus leading to spin polarized current. This phenomenon is known as the chiral induced spin selectivity (CISS) effect. One of the most surprising experimental results recently demonstrated is that magnetization reversal in a ferromagnet (FM) with perpendicular anisotropy can be realized solely by chemisorbing a chiral molecular monolayer without applying any current or external magnetic field. This result raises the currently open question of whether this effect is due to the bonding event, held by the ferromagnet, or a long timescale effect stabilized by exchange interactions. In this work we have performed vectorial magnetic field measurements of the magnetization reorientation of a ferromagnetic layer exhibiting perpendicular anisotropy due to CISS using nitrogen-vacancy centers in diamond, and followed the time dynamics of this effect. In parallel, we have measured the molecular monolayer tilt angle in order to find a correlation between the time dependence of the magnetization re-orientation and the change of the tilt angle of the molecular monolayer. We have identified that changes in the magnetization direction correspond to changes of the molecular monolayer tilt angle, providing evidence for a long-timescale characteristic of the induced magnetization reorientation. This suggests that the CISS effect has an effect over long-timescales which we attribute to exchange interactions. These results offer significant insights into the fundamental processes underlying the CISS effect, contributing to the implementation of CISS in state-of-the-art applications such as spintronic and magnetic memory devices.

cond-mat.mes-hall↗
arXiv2020

Structure-based Hamiltonian model for IsiA uncovers a highly robust pigment protein complex

The iron stress-induced protein A (IsiA) is a source of interest and debate in biological research. The IsiA super-complex, binding over 200 chlorophylls, assembles in multimeric rings around photosystem I (PSI). Recently, the IsiA-PSI structure was resolved to 3.48 Å. Based on this structure, we created a model simulating a single excitation event in an IsiA monomer. This model enabled us to calculate the fluorescence and the localisation of the excitation in the IsiA structure. To further examine this system, noise was introduced to the model in two forms -- thermal and positional. Introducing noise highlights the functional differences in the system between cryogenic temperatures and biologically relevant temperatures. Our results show that the energetics of the IsiA pigment-protein complex are very robust at room temperature. Nevertheless, shifts in the position of specific chlorophylls lead to large changes in their optical and fluorescence properties. Based on these results we discuss the implication of highly robust structures, with potential for serving different roles in a context dependent manner, on our understanding of the function and evolution of photosynthetic processes.

physics.bio-ph↗
arXiv2020

An analytic model of chiral-induced spin selectivity

Organic materials are known to feature long spin-diffusion times, originating in a generally small spin-orbit coupling observed in these systems. From that perspective, chiral molecules acting as efficient spin selectors pose a puzzle, that attracted a lot of attention during the recent years. Here we revisit the physical origins of chiral-induced spin selectivity (CISS), and propose a simple analytic minimal model to describe it. The model treats a chiral molecule as an anisotropic wire with molecular dipole moments aligned arbitrarily with respect to the wire's axes, and is therefore quite general. Importantly, it shows that helical structure of the molecule is not necessary to observe CISS and other chiral non-helical molecules can also be considered as a potential candidates for CISS effect. We also show that the suggested simple model captures the main characteristics of CISS observed in experiment, without the need for additional constraints employed in the previous studies. The results pave the way for understanding other related physical phenomena where CISS effect plays an essential role.

cond-mat.mes-hall↗
arXiv2019

Magnetic-Related States and Order Parameter Induced in a Conventional Superconductor by Nonmagnetic Chiral Molecules

Hybrid ferromagnetic/superconducting systems are well known for hosting intriguing phenomena such as emergent triplet superconductivity at their interfaces and the appearance of in-gap, spin polarized Yu-Shiba-Rusinov (YSR) states bound to magnetic impurities on a superconducting surface. In this work we demonstrate that similar phenomena can be induced on a surface of a conventional superconductor by chemisorbing non-magnetic chiral molecules. Conductance spectra measured on NbSe2 flakes over which chiral alpha helix polyalanine molecules were adsorbed, exhibit, in some cases, in-gap states nearly symmetrically positioned around zero bias that shift with magnetic field, akin to YSR states, as corroborated by theoretical simulations. Other samples show evidence for a collective phenomenon of hybridized YSR-like states giving rise to unconventional, possibly triplet superconductivity, manifested in the conductance spectra by the appearance of a zero bias conductance that diminishes, but does not split, with magnetic field. The transition between these two scenarios appears to be governed by the density of adsorbed molecules.

cond-mat.supr-con↗
arXiv2019

Unconventional order parameter induced by helical chiral molecules adsorbed on a metal proximity-coupled to a superconductor

Following our previous results, which provide evidence for the emergence of a chiral p-wave triplet-pairing component in superconducting Nb upon the adsorption of chiral molecules, we turned to investigate whether such an effect can take place in a proximal superconductor consisting of metal on superconductor bilayer. Note that in such proximity systems, correlated electron-hole (Andreev) pairs exist in the normal metal rather than genuine Cooper pairs. To that end, we used scanning tunneling spectroscopy (STS) on thin Au films grown in-situ on NbN (a conventional s-wave superconductor) before and after adsorbing helical chiral, alpha-helix polyalanine molecules. The tunneling spectra measured on the pristine Au surface showed conventional (s-wave like) proximity gaps. However, upon molecules adsorption the spectra significantly changed, all exhibiting a zero-bias conductance peak embedded inside a gap, indicating unconventional superconductivity. The peak reduced with magnetic field but did not split, consistent with equal-spin triplet-pairing p-wave symmetry. In contrast, adsorption of non-helical chiral cysteine molecules did not yield any apparent change in the order parameter, and the tunneling spectra exhibited only gaps free of in-gap structure.

cond-mat.supr-con↗
arXiv2018

Four-wave mixing and nonlinear parameter measurement in a gallium-nitride ridge waveguide

Gallium-nitride (GaN) is a promising material platform for integrated electro-optic devices due to its wide direct bandgap, pronounced nonlinearities and high optical damage threshold. Low-loss ridge waveguides in GaN layers were recently demonstrated. In this work we provide a first report of four-wave mixing in a GaN waveguide at telecommunication wavelengths, and observe comparatively high nonlinear propagation parameters. The nonlinear coefficient of the waveguide is measured as 1.6 +/- 0.45 [W*m]-1, and the corresponding third-order nonlinear parameter of GaN is estimated as 3.4e-18 +/- 1e-18 [m^2/W]. The results suggest that GaN waveguides could be instrumental in nonlinear-optical signal processing applications.

physics.optics↗
arXiv2017

Light Adaptation in Phycobilisome antennas: Influence on the Rod Length and Structural Arrangement

Phycobilisomes, the light-harvesting antennas of cyanobacteria, can adapt to a wide range of environments thanks to a composition and function response to stress conditions. We study how structural changes influence excitation transfer in these super-complexes. Specifically, we show the influence of the rod length on the photon absorption and subsequent excitation transport to the core. Despite the fact that the efficiency of individual disks on the rod decreases with increasing rod length, we find an optimal length for which the average rod efficiency is maximal. Combining this study with experimental structural measurements, we propose models for the arrangement of the phycobiliproteins inside the thylakoid membranes, evaluate the importance of rod length, and predict the corresponding transport properties for different cyanobacterial species. This analysis, which links the functional and structural properties of full phycobilisome complexes, thus provides further rationals to help resolving their exact structure.

physics.chem-ph↗
arXiv2017

Regulating the Energy Flow in a Cyanobacterial Light Harvesting Antenna Complex

Photosynthetic organisms harvest light energy, utilizing the absorption and energy transfer properties of protein-bound chromophores. Controlling the harvesting efficiency is critical for the optimal function of the photosynthetic apparatus. Here, we show that cyanobacterial light-harvesting antenna may be able to regulate the flow of energy in order to switch reversibly from efficient energy conversion to photo-protective quenching via a structural change. We isolated cyanobacterial light harvesting proteins, phycocyanin and allophycocyanin, and measured their optical properties in solution and in an aggregated-desiccated state. The results indicate that energy band structures are changed, generating a switch between two modes of operation: exciton transfer and quenching; achieved without dedicated carotenoid quenchers. This flexibility can contribute greatly to the large dynamic range of cyanobacterial light harvesting systems.

physics.bio-ph↗
arXiv2013

Self-assembling hybrid diamond-biological quantum devices

The realization of scalable arrangements of nitrogen vacancy (NV) centers in diamond remains a key challenge on the way towards efficient quantum information processing, quantum simulation and quantum sensing applications. Although technologies based on implanting NV-center in bulk diamond crystals or hybrid device approaches have been developed, they are limited in the achievable spatial resolution and by the intricate technological complexities involved in achieving scalability. We propose and demonstrate a novel approach for creating an arrangement of NV-centers, based on the self-assembling capabilities of biological systems and its beneficial nanometer spatial resolution. Here, a self-assembled protein structure serves as a structural scaffold for surface functionalized nanodiamonds, in this way allowing for the controlled creation of NV-structures on the nanoscale and providing a new avenue towards bridging the bio-nano interface. One-, two- as well as three-dimensional structures are within the scope of biological structural assembling techniques. We realized experimentally the formation of regular structures by interconnecting nanodiamonds using biological protein scaffolds. Based on the achievable NV-center distances of 11nm, we evaluate the expected dipolar coupling interaction with neighboring NV-center as well as the expected decoherence time. Moreover, by exploiting these couplings, we provide a detailed theoretical analysis on the viability of multiqubit quantum operations, suggest the possibility of individual addressing based on the random distribution of the NV intrinsic symmetry axes and address the challenges posed by decoherence and imperfect couplings. We then demonstrate in the last part that our scheme allows for the high-fidelity creation of entanglement, cluster states and quantum simulation applications.

quant-ph↗
arXiv2011

Increased superconducting transition temperature of a niobium thin-film proximity-coupled to gold nanoparticles using linking organic molecules

The superconducting critical temperature, TC, of thin Nb films is significantly modified when gold nanoparticles (NPs) are chemically linked to the Nb film, with a consistent enhancement when using 3 nm long disilane linker molecules. The TC increases by up to 10% for certain linker length and NPs size. No change is observed when the nanoparticles are physisorbed with non-linking molecules. Electron tunneling spectra acquired on the linked NPs below TC typically exhibit zero-bias peaks. We attribute these results to a pairing mechanism coupling electrons in the Nb and the NPs, mediated by the organic linkers.

cond-mat.supr-con↗