Spin Properties Research Articles

Spin-Dependent Regulation of The Electronic and Magnetic Properties of Poly(3-Alkylthiophene) Oligomers and Their Composites with Aromatic Nanoadditives

The energy and spin parameters of poly(3-alkylthiophene) oligomers and their composites with aromatic hydrocarbons are calculated. The coexistence of polarons with different degrees of delocalization in the studied compounds has been identified. Periodic changes in the electronic and spin properties of composites were detected, initiated by the interaction of oligomers with aromatic nanoadditives. The anisotropic parameters of the spin Hamiltonians of the studied systems are obtained and their high-resolution EPR spectra are calculated.

Spin-bearing molecules as optically addressable platforms for quantum technologies

Abstract Efforts to harness quantum hardware relying on quantum mechanical principles have been steadily progressing. The search for novel material platforms that could spur the progress by providing new functionalities for solving the outstanding technological problems is however still active. Any physical property presenting two distinct energy states that can be found in a long-lived superposition state can serve as a quantum bit (qubit), the basic information processing unit in quantum technologies. Molecular systems that can feature electron and/or nuclear spin states together with optical transitions are one of the material platforms that can serve as optically addressable qubits. The attractiveness of molecular systems for quantum technologies relies on the fact that molecular structures of atomically defined nature can be obtained in endless diversity of chemical compositions. Crucially, by harnessing the molecular design protocols, the optical and spin (electronic and nuclear) properties of molecules can be tailored, aiding the design of optically addressable spin qubits and quantum sensors. In this contribution, we present a concise and collective discussion of optically addressable spin-bearing molecules – namely, organic molecules, transition metal (TM) and rare-earth ion (REI) complexes – and highlight recent results such as chemical tuning of optical and electron spin quantum coherence, optical spin initialization and readout, intramolecular quantum teleportation, optical coherent storage, and photonic-enhanced optical addressing. We envision that optically addressable spin-carrying molecules could become a scalable building block of quantum hardware for applications in the fields of quantum sensing, quantum communication and quantum computing.

Investigation of PCVSi− defect in 4H–SiC as a candidate for a qubit

Abstract Exploration of spin defects in semiconductors for possible qubits encourages the development of the quantum field. Silicon carbide (SiC) is a suitable platform to carry spin defects, due to its excellent electrical, mechanical and optical properties, together with its convenience for crystallographic growth and doping processes. In this study, a negatively charged phosphorus-vacancy (PCVSi −) defect, consisting of a silicon vacancy and nearby substitution of a phosphorus atom to a carbon atom in 4H–SiC, is investigated by first-principles calculations. This defect is demonstrated to possess a high spin (S = 1) with relatively low formation energy. Computed zero-phonon line energy and zero-field splitting parameters of this defect are close to those of neutral divacancy (VCVSi 0), negatively charged nitrogen-vacancy center (NCVSi −) and some other color centers, which indicate a similarity of both optical and spin properties among them. Moreover, the electron spin coherence time of this defect turns out to be 1.15–1.40 ms. Such a long coherence time provides the defect with reliability for quantum information processing. Our results show that the PCVSi − defect can be a promising candidate for a qubit.

Long-term evolution of spin and other properties of neutron star low-mass X-ray binaries: implications for millisecond X-ray pulsars

ABSTRACT A neutron star (NS) accreting matter from a companion star in a low-mass X-ray binary (LMXB) system can spin up to become a millisecond pulsar (MSP). Properties of many such MSP systems are known, which is excellent for probing fundamental aspects of NS physics when modelled using the theoretical computation of NS LMXB evolution. Here, we systematically compute the long-term evolution of NS, binary, and companion parameters for NS LMXBs using the stellar evolution code mesa. We consider the baryonic to gravitational mass conversion to calculate the NS mass evolution and show its cruciality for the realistic computation of some parameters. With computations using many combinations of parameter values, we find the general nature of the complex NS spin frequency ($\nu$) evolution, which depends on various parameters, including accretion rate, fractional mass-loss from the system, and companion star magnetic braking. Further, we utilize our results to precisely match some main observed parameters, such as $\nu$, orbital period ($P_{\rm orb}$), etc., of four accreting millisecond X-ray pulsars (AMXPs). By providing the $\nu$, $P_{\rm orb}$, and the companion mass spaces for NS LMXB evolution, we indicate the distribution and plausible evolution of a few other AMXPs. We also discuss the current challenges in explaining the parameters of AMXP sources with brown dwarf companions and indicate the importance of modelling the transient accretion in LMXBs as a possible solution.

Single-Shot Readout and Weak Measurement of a Tin-Vacancy Qubit in Diamond

The negatively charged tin-vacancy center in diamond (SnV−) is an emerging platform for building the next generation of long-distance quantum networks. This is due to the SnV−’s favorable optical and spin properties including bright emission, insensitivity to electronic noise, and long spin coherence times at temperatures above 1 K. Here, we demonstrate measurement of a single SnV− electronic spin with a single-shot readout fidelity of 87.4%, which can be further improved to 98.5% by conditioning on multiple readouts. In the process, we develop understanding of the relationship between strain, magnetic field, spin readout, and microwave spin control. We show that high-fidelity readout is compatible with rapid microwave spin control, demonstrating a favorable parameter regime for use of the SnV− center as a high-quality spin-photon interface. Finally, we use weak quantum measurement to study measurement-induced dephasing; this illuminates the fundamental interplay between measurement and decoherence in quantum mechanics, and provides a universal method to characterize the efficiency of color-center spin readout. Taken together, these results overcome an important hurdle in the development of the SnV−-based quantum technologies and, in the process, develop techniques and understanding broadly applicable to the study of solid-state quantum emitters. Published by the American Physical Society 2024

The phonon-modulated Jahn–Teller distortion of the nitrogen vacancy center in diamond

The negatively charged nitrogen vacancy (NV) center in diamond is an optically accessible material defect with a unique combination of spin and optical properties that has attracted interest in quantum-information sciences and as a design candidate for nanoscale quantum sensors. Here, we present time-resolved nonlinear optical spectroscopy measurements, conducted with ultrabroadband laser pulses, that reveal strong modulation of the excited-state by the longitudinal optical (LO) phonon of the diamond lattice. The LO phonon and its overtones geometrically distort neighboring NV centers, driving long lived (3.5 ps) excited state relaxation of coupled NV centers after the initial excitation and ultrafast (<150 fs) decay of the Jahn–Teller distortion. These observations elevate the LO phonon to an important tuning mode of the Jahn–Teller conical intersection and help resolve previous spectroscopy experiments that noted longer-lived excited-state dynamics.

First-principles computational methods for quantum defects in two-dimensional materials: A perspective

Quantum defects are atomic defects in materials that provide resources to construct quantum information devices such as single-photon emitters and spin qubits. Recently, two-dimensional (2D) materials gained prominence as a host of quantum defects with many attractive features derived from their atomically thin and layered material formfactor. In this Perspective, we discuss first-principles computational methods and challenges to predict the spin and electronic properties of quantum defects in 2D materials. We focus on the open quantum system nature of the defects and their interaction with external parameters such as electric field, magnetic field, and lattice strain. We also discuss how such prediction and understanding can be used to guide experimental studies, ranging from defect identification to tuning of their spin and optical properties. This Perspective provides significant insights into the interplay between the defect, the host material, and the environment, which will be essential in the pursuit of ideal two-dimensional quantum defect platforms.

Luminescent Organic Triplet Diradicals as Optically Addressable Molecular Qubits.

Optical-spin interfaces that enable the photoinitialization, coherent microwave manipulation, and optical read-out of ground state spins have been studied extensively in solid-state defects such as diamond nitrogen vacancy (NV) centers and are promising for quantum information science applications. Molecular quantum bits (qubits) offer many advantages over solid-state spin centers through synthetic control of their optical and spin properties and their scalability into well-defined multiqubit arrays. In this work, we report an optical-spin interface in an organic molecular qubit consisting of two luminescent tris(2,4,6-trichlorophenyl)methyl (TTM) radicals connected via the meta-positions of a phenyl linker. The triplet ground state of this system can be photoinitialized in its |T0⟩ state by shelving triplet populations as singlets through spin-selective excited-state intersystem crossing with 80% selectivity from |T+⟩ and |T-⟩. The fluorescence intensity in the triplet manifold is determined by the ground-state polarization, and we show successful optical read-out of the ground-state spin following microwave manipulations by fluorescence-detected magnetic resonance spectroscopy. At 85 K, the lifetime of the polarized ground state is 45 ± 3 μs, and the ground state phase memory time is Tm = 5.9 ± 0.1 μs, which increases to 26.8 ± 1.6 μs at 5 K. These results show that luminescent diradicals with triplet ground states can serve as optically addressable molecular qubits with long spin coherence times, which marks an important step toward the rational design of spin-optical interfaces in organic materials.

Electronic structure of ultrathin single-walled platinum nanotubes

Using Density Functional Theory based on the plane wave method and linearized augmented cylindrical wave method, and taking into account the spin–orbit interaction, the structural, electronic and spin properties of ultrathin single-walled nanotubes consisting of six platinum rows are obtained. The nanotubes are found to possess metallic electronic mobility, including the nonchiral Pt(6,0) with the largest number (15G0) of ballistic channels. Analysis of the density of electronic states at Fermi level revealed that the chiral Pt(5,1) has a difference in concentration of mobile electrons with opposite spins of 1.42 times, and up to 3–4 times under a weak torsional strain.

Physics-Guided Machine Learning for Satellite Spin Property Estimation from Light Curves

Physics-Guided Machine Learning for Satellite Spin Property Estimation from Light Curves

Magnetic Excitations in Ferromagnetically Coupled Spin-1 Nanographenes.

In the pursuit of high-spin building blocks for the formation of covalently bonded 1D or 2D materials with controlled magnetic interactions, -electron magnetism offers an ideal framework to engineer ferromagnetic interactions between nanographenes. As a first step in this direction, we explore the spin properties of ferromagnetically coupled triangulenes-triangular nanographenes with spin . By combining in-solution synthesis of rationally designed molecular precursors with on-surface synthesis, we successfully achieve covalently bonded triangulene dimers and trimers on Au(111). Starting with the triangulene dimer, we meticulously characterize its low-energy magnetic excitations using inelastic electron tunneling spectroscopy (IETS). IETS reveals conductance steps corresponding to a quintet-to-triplet excitation, and a zero-bias peak resulting from higher-order spin-spin scattering of the five-fold degenerate ferromagnetic ground state. The Heisenberg model captures the key parameters of inter-triangulene ferromagnetic exchange, and its successful extension to the larger system validates the model's accuracy. We anticipate that incorporating ferromagnetically coupled building blocks into the repertoire of magnetic nanographenes will unlock new possibilities for designing carbon nanomaterials with complex magnetic ground states.

Measurement of the Breaking Indices of Frequently Ghtching Pulsars using Integration Method

Pulsars are old, stellar objects that emit electromagnetic radiations in a definite time interval, with a predictable smooth spin-down, predisposed to discrete fluctuations/glitches. The rotational frequency of pulsars decays with time as quantified by the breaking index which is now known to have no consequence on other pulsar qualities like obliquity angle evolution or complex high-order multiple structures but rather on its spin proportion. In the canonical model n=3, but observationally n≠3 in numerous cases. Showing that the canonical model requires modification. Using the Australian Telescope National Facility (ATNF). Pulsars catalog, we selected 208 pulsars with 670 glitches. We computed the breaking and observed that the breaking index is smaller for very young pulsars, which usually glitch more frequently than their older, more stable counterpart analysis. They have switched over from time and also account for over 68% of the entire glitches in our population. A regression analysis shows that spin properties of pulsars are ≥ 65% correlated with breaking index (n). Implications of this result are discussed.

Coherent spin dynamics between electron and nucleus within a single atom

The nuclear spin, being much more isolated from the environment than its electronic counterpart, presents opportunities for quantum experiments with prolonged coherence times. Electron spin resonance (ESR) combined with scanning tunnelling microscopy (STM) provides a bottom-up platform to study the fundamental properties of nuclear spins of single atoms on a surface. However, access to the time evolution of nuclear spins remained a challenge. Here, we present an experiment resolving the nanosecond coherent dynamics of a hyperfine-driven flip-flop interaction between the spin of an individual nucleus and that of an orbiting electron. We use the unique local controllability of the magnetic field emanating from the STM probe tip to bring the electron and nuclear spins in tune, as evidenced by a set of avoided level crossings in ESR-STM. Subsequently, we polarize both spins through scattering of tunnelling electrons and measure the resulting free evolution of the coupled spin system using a DC pump-probe scheme. The latter reveals a complex pattern of multiple interfering coherent oscillations, providing unique insight into hyperfine physics on a single atom level.

Magnetic and thermodynamic properties of mixed spin-3/2 and spin-3 Ising ferrimagnets on a 2D triangular lattice: Monte Carlo study

Monte Carlo methods in the presence and absence of an external magnetic field were used to investigate the thermodynamic and magnetic properties of the mixed spins (3/2, 3) Ising ferrimagnets in a 2D triangular lattice consisting of sublattices A, B, and C. Two types of mixing were considered: S→=(SA,SB,SC)=(3/2,3,3) (Model I) and S→=(SA,SB,SC)=(3/2,3,3/2) (Model II). In contrast to bipartite lattices, the antiferromagnetic coupling between spin-3/2 and spin-3 in the triangular lattice leads to geometric frustrations that impact magnetic properties. Determination of ground state phase diagrams, combined with verification of whether or not there was magnetic hysteresis when crossing each transition line, revealed first- and second-order phase transition lines, as well as multicritical points. The temperature investigation in the absence of an external magnetic field revealed rich magnetic properties such as 1st- and 2nd-order phase transitions, N- and L-type compensation points, tricritical points, and critical endpoints, as well as M-, P-, Q-, R- and S-type total magnetization behaviours. The effect of the crystal field on finite-temperature phase diagrams and compensation behaviour was also carried out. As a result, the critical temperatures of Model II become constant when the crystal field is sufficiently strong. In contrast, several critical values of the crystal field for which the critical temperature is zero were identified for Model I. In the presence of a magnetic field, hysteresis behaviour and associated magnetic properties such as coercivity and magnetic remanence were investigated. The effect of crystal field and temperature was explored. Hysteresis of one to four loops were found at low temperatures when the crystal field varied. Finally, as the temperature rises, the hysteresis loops' area decreases to zero at high temperatures.

Rare Earth‐Diamond Hybrid Structures for Optical Quantum Technologies

AbstractDiamond containing nitrogen‐vacancy centers (NV−) is one of the most investigated materials for quantum technologies, because of this system's exceptional spin properties. Although the NV− optical transition is very bright, it suffers from spectral diffusion and weak zero‐phonon line, and is in the visible range. This limits integration into quantum photonic structures and interfacing with optical fiber networks. In contrast, rare earth (RE) ions exhibit extremely narrow and stable optical transitions, including erbium's 1.5 µm telecom wavelength. Combining RE with NV− properties through short‐range interactions is however challenging as RE do not readily enter the diamond lattice. In this work, a thin‐film‐based architecture in which RE and NV− centers can interact while preserving their unique properties is introduced. Thin films of Er3+:Y2O3 are grown by chemical vapor deposition on diamond substrates with well‐crystallized and highly textured structures. An extensive spectroscopic study of Er3+ transitions at room and low temperatures further reveals that photoluminescence spectra and decays are close to bulk materials. It is also shown that Y2O3 thin film deposition has no detrimental effects on NV− optical and spin properties. RE thin films deposited on diamond can thus be suitable for building hybrid materials for new functionalities in quantum sensing, communication, and processing.

Antioxidant Activity of MgSO4 Ion Pairs by Spin-Electron Stabilization of Hydroxyl Radicals through DFT Calculations: Biological Relevance.

Magnesium sulfate has been of great interest as an antioxidant for its ability to decrease the oxidizing capacity of the hydroxyl radical. Previously, it was shown that the contact ion pair of this salt could stabilize •OH by coordinating with Mg and delocalizing the unpaired electron over sulfate. The present study explores in detail the MgSO4 antioxidant properties, considering all its ion pairs with •OH in different conformations. The analyses were based on structural, spin, and energetic properties using the DFT approach. As a result, the high antioxidant potential of MgSO4 is related to the spin-electron transfer from SO4 -2 to •OH causing electron spin delocalization and electrostatic stabilization. This transfer occurs for all ion pairs when •OH approaches the Mg first solvation shell, without being coordinated to Mg. The direct Mg-•OH interaction further stabilizes the radical system. These results show that spin-electron transfers are feasible in all hydrated ion pairs MgSO4-•OH, even at a •OH-sulfate distance greater than 10 Å.

The effect of metal-to-ligand charge transfer on linear and nonlinear optical properties of hexaphyrin and metallo-hexaphyrins

Charge transfer from metal to ligand has implications in various fields of chemistry, physics and biology. The manipulation of spin properties would be necessary for controlling charge transfer in spintronics and biological applications. Upon binding to the metal atoms (Ni, Cu, Au, etc.), the spin properties would be modulated in organic conjugated molecules of less intrinsic spin–orbit coupling (SOC) due to SOC coming from the heavy elements. Emission spectra calculation is necessary to validate them as suitable fluorescence quenchers. The nonlinear optical properties like first-order hyperpolarisability β and second-order hyperpolarisability γ calculations are important to find out their relation between fluorescence quenching and higher order nonlinear optical (NLO) properties. From the second-order NLO properties, we computed degenerate four-wave mixing (DFWM) component ( γ ( 2 ) ( − ω ; ω , ω , − ω )) and finally quadratic nonlinear refractive indices of the expanded porphyrins (EPs). How the linear and nonlinear optical properties are dependent on the SOC coming from the heavy materials (Ni, Cu, Au), and charge transfer process is the most interesting question to be addressed for their potential uses for various optoelectronic and spintronic applications.

Optical and Electrical Properties of Spin Coated Bilayer Graphene

Graphene is a 2D material with high transparency, high carrier mobility, and high electrical conductivity [1-4]. In this work, a thin graphene layer was coated on Si through spin coating, and dip coating technique.Graphene ink was prepared by expanding the graphite flakes through microwave irradiation followed by ultrasonic liquid phase exfoliation. 5 mg of the resulting graphene was dispersed in 1 ml of IPA through a probe sonication technique to obtain the graphene suspension/ink. To form the graphene/Si junction, pieces of 3 x 3 cm2 of n-type Si were used. In addition, same size of fused silica were used to measure the reflectance of deposited graphene. The graphene layer in the first sample was formed by spin coating 40 µl of graphene ink on the Si and the fused silica at a speed of 200 rpm for 40 s. The second sample was prepared by dip coating technique, where 13 ml of the graphene ink was added to 47 ml of IPA, followed by dipping Si and the fused silica pieces with a speed of 20 mm/min till they immersed completely and were kept for 1 min and were moved up at the same speed and dried at room temperature. This dip-coating process was repeated 10 times for each sample.The morphology of graphene-coated area was analyzed using the SEM technique. The SEM images of the spin-coated shows that the surface is fully covered with graphene flakes of different sizes stacked on each other with varied orientations, this shows the ability to obtain a continuous coating of graphene by spin coating. Also, Hall effect measurements were performed, and it showed that the conductivity of the Si substrate was 1.95x10-2 ohm-1cm-1, and it increased to 2.74 ohm-1cm-1 after adding the graphene. Finally, the reflectance of the graphene on fused silica was measured using a UV-VIS spectrophotometer, and it showed that the reflectance decreased from 8% to 4% in the range from 360 to 860 nm after adding the graphene.For dip-coated sample, the SEM image shows some voids, and empty areas linked with by graphene structure with a width of few microns, this shows that the dip-coating process needs to be optimized to get a full coverage of the surface. The electrical measurement of this sample showed that the conductivity increased to 2.66 ohm-1cm-1 after the dip coating of graphene. For the reflectance measurements, it was observed that the graphene has decreased the reflectance to 6-7% in the range from 360 to 860 nm.Finally, spin coating at higher speed, and less amount of graphene can be tested, to obtain a thinner graphene layer. For the dip coating process, higher graphene concentration in IPA, and longer immersion time will be investigated to get a better coverage.

Understanding the Reaction Activity of Ni(1-x)FexOH Towards Oxygen Evolution Reaction

The development of electrocatalysts towards the oxygen evolution reaction based on earth-abundant and cheap materials, such as transition metal oxide and hydroxide, is crucial to reduce the emission of CO2 and slowdown the global warming [1]. Among these transition metal compounds, ferromagnetic electrocatalysts usually exhibit promising activities towards OER due to their unique electron spin properties [2]. Applying an external magnetic field can further tune the electron spin polarization of ferromagnetic materials and, therefore, improve the OER activity. However, evaluating the activity of these electrocatalysts towards OER remains challenging. For example, the electrocatalysts will undergo activation under reaction conditions (frequently due to Fe insertion), which brings difficulties in determining the real reaction sites as well as establishing the “structure-activity” relationship [3]. In addition, the overall measure activity (current density) is contributed by multiple factors such as intrinsic kinetics, mass transfer, conductivity, etc., which strongly depend on operation conditions. In this talk, I will present our recent study of OER on Ni(1-x)FexOH [4]. Electrochemical impedance spectroscopy (EIS) and quasi-in situ XPS will be applied to obtain the contribution from different reaction parameters and understand the intrinsic activity.[1] McCrory, C. C. L. et al. Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices. Am. Chem. Soc. 137, 4347–4357 (2015).[2] Ren, X. et al. Spin-polarized oxygen evolution reaction under magnetic field. Commun. 12, 1–12 (2021).[3] Jung, S., McCrory, C. C. L., Ferrer, I. M., Peters, J. C. & Jaramillo, T. F. Benchmarking nanoparticulate metal oxide electrocatalysts for the alkaline water oxidation reaction. Mater. Chem. A 4, 3068–3076 (2016)[4] Wei Chen, Laura Donk, Tiago Fernandes, Anna Kitayev, ErvinTal Gutelmacher, Yury V. Kolen’ko, Marta C. Figueiredo*, in preparation.

Diagnostics of Alzheimer’s disease using fluorescent nanodiamond-based spin-enhanced lateral flow immunoassay

Fluorescent nanodiamond (FND) has been regarded as a superior alternative reporter for lateral flow immunoassays. The negatively charged nitrogen-vacancy (NV−) center in FND is a point defect with unique magneto-optical properties, giving outstanding characteristics to detect biomarkers of diseases, including Alzheimer’s disease (AD). AD is the most common form of dementia, which might ultimately result in complete brain failure and, eventually, death. The two most commonly used techniques to detect brain changes caused by AD are brain imaging and lumbar puncture. However, brain imaging and lumbar puncture are costly and time-consuming. Thus, we have developed Spin-Enhanced Lateral Flow Immunoassay (SELFIA) for in vitro AD diagnostics utilizing the electron spin properties of the NV−-centers in FND to achieve background-free ultrasensitive detection. To detect the pTau protein (a critical AD biomarker), we first conjugated FND to anti-pTau antibodies through non-covalent conjugation. We employed a sandwich assay to enhance sensitivity and specificity by immobilizing capture antibodies on the membrane so that antibody-antigen–antibody immunocomplexes would be formed. Our FND-based SELFIA only requires approximately 30 min to reach a detection limit of 7 pg/mL, where the threshold for positivity was 101.95 pg/mL for cerebrospinal fluid pTau217. This is the first study that utilized FND-based SELFIA for AD detection. The current SELFIA platform is rapid, easy to use, and affordable. This study not only represents a significant innovation but also opens new avenues for early diagnosis and treatment strategies.