Spin Interactions Research Articles

Higher order spin interactions mediated by the substrate

Higher order spin interactions mediated by the substrate

Description of the odd 249−253No nuclei using Skyrme functionals with modified spin–spin interaction

The Skyrme energy-density functionals with modified spin–spin interaction and pairing strength are used for description of the [Formula: see text]No, [Formula: see text]No and [Formula: see text]No excited states. The results of the HFB and cranked HFB calculations taking into account the blocking effect are in reasonable agreement with the available data. For many states, including rotational and three-quasiparticle states, the results of self-consistent calculations were obtained for the first time.

Hawking-Page transition on a spin chain

The accessibility of the Hawking-Page transition in AdS5 through a one-dimensional (1D) Heisenberg spin chain is demonstrated. We use the random matrix formulation of the Loschmidt echo for a set of spin chains, and randomize the ferromagnetic spin interaction. It is shown that the thermal Loschmidt echo, when averaged, detects the predicted increase in entropy across the Hawking-Page transition. This suggests that a 1D spin chain exhibits characteristics of black hole physics in 4+1 dimensions. We show that this approach is equally applicable to free fermion systems with a general dispersion relation. Published by the American Physical Society 2024

SPT extension of Z2 quantum Ising model's ferromagnetic phase

This paper focuses on the creation of a model with explicitly defined symmetry-protected topological (SPT) phases on a triangular lattice as an extension of Z2 Ising model's ferromagnetic phase. Unlike in previously known similar works, this model is based on an initially interacting system which is known to describe experimentally realizable physical systems. The Hamiltonian for these edge states contains four-point spin interactions between next-to-next nearest neighbors. As an initially interacting A generic technique for creating SPT models is developed, allowing for the construction of translation-invariant edge models.

Quantitative analysis of the slow exchange process by 19F NMR in the presence of scalar and dipolar couplings: applications to the ribose 2'-19F probe in nucleic acids.

Solution NMR spectroscopy is a particularly powerful technique for characterizing the functional dynamics of biomolecules, which is typically achieved through the quantitative characterization of chemical exchange processes via the measurement of spin relaxation rates. In addition to the conventional nuclei such as 15N and 13C, which are abundant in biomolecules, fluorine-19 (19F) has recently garnered attention and is being widely used as a site-specific spin probe. While 19F offers the advantages of high sensitivity and low background, it can be susceptible to artifacts in quantitative relaxation analyses due to a multitude of dipolar and scalar coupling interactions with nearby 1H spins. In this study, we focused on the ribose 2'-19F spin probe in nucleic acids and investigated the effects of 1H-19F spin interactions on the quantitative characterization of slow exchange processes on the millisecond time scale. We demonstrated that the 1H-19F dipolar coupling can significantly affect the interpretation of 19F chemical exchange saturation transfer (CEST) experiments when 1H decoupling is applied, while the 1H-19F interactions have a lesser impact on Carr-Purcell-Meiboom-Gill relaxation dispersion applications. We also proposed a modified CEST scheme to alleviate these artifacts along with experimental verifications on self-complementary RNA systems. The theoretical framework presented in this study can be widely applied to various 19F spin systems where 1H-19F interactions are operative, further expanding the utility of 19F relaxation-based NMR experiments.

Analyzing trade-off issues in synthesis of magnetic polymer compounds through theoretical investigation

Incorporating magnetic species, magnetic functional groups or additives, into polymer hosts is an effective method for synthesizing magnetic polymers. Polymers can gain magnetic moments not solely through magnetic coupling but also via the induction of Coulombic excitation. Attachment of the magnetic side-groups to the polymer backbone increases orbital localization in repeat units. This will bring two competing effects. The orbital localization will increase the intra-site Coulomb interaction, which increases magnetic moments in repeat units. Oppositely, the orbital localization also increases the energy splitting between orbitals on the polymer backbone and on side-groups, suppressing thus the magnetic moments of repeat units. However, a preference for low-spin states in the polymer units emerges when a substantial split in orbital energy occurs due to a strong coupling, consequently suppressing the magnetic moment. On the contrary, a minimal split in orbital energy within the polymer units can readily induce a high-spin state and generate a magnetic moment. However, in such cases, the Coulomb interaction triggered by the interconnected magnetic moieties might be too weak to produce a magnetic moment in the polymer. To explore this trade-off, we have proposed a theoretical two-level model aimed at elucidating the decision-making process of experimentalists during the synthesis of magnetic polymers. We also found that the dimerization of the polymer backbone together with the phonon dependence of spin–spin interaction between near-neighbor repeat units increases magnetic moments. As the magnetic responses arising from Coulombic interactions in polymers are intricately linked to carrier density, properties of the magnetic polymers acting as an active layer of a field-effect transistor can be tuned by the gate field, which controls the charge carrier density in the transistor transport channel.

In Situ‐Tunable Spin–Spin Interactions in a Penning Trap with In‐Bore Optomechanics

AbstractExperimental implementations of quantum simulation must balance control‐field‐induced decoherence with the controllability of the quantum system. The ratio of coherent interaction strength to decoherence induced by stimulated emission in atomic systems is typically determined by hardware constraints, limiting the flexibility needed to explore different operating regimes. Here, an optomechanical system is presented for in situ tuning of the coherent spin‐motion and spin‐spin interaction strength in 2D ion crystals in a Penning trap. Enabled by precision closed‐loop piezo‐actuated positioners integrated into the confined space of a superconducting magnet's bore, the system allows tuning of the angle‐of‐incidence of Raman laser beams up to , governing the ratio of coherent to incoherent light‐matter interaction for fixed optical power. System characterization involves measurements of the induced mean‐field spin precession under the application of an optical dipole force in ion crystals cooled below the Doppler limit through electromagnetically induced transparency cooling. These experiments show approximately a variation in the coherent to incoherent interaction ratio with changing , consistent with theoretical predictions. The system stability is characterized over 6000 s, resulting in a drift rate of h–1. These technical developments will be crucial in future quantum simulations and sensing applications.

Relativistic Douglas–Kroll–Hess calculations of hyperfine interactions within first-principles multireference methods

A relativistic magnetic hyperfine interaction Hamiltonian based on the Douglas–Kroll–Hess (DKH) theory up to the second order is implemented within the ab initio multireference methods, including spin–orbit coupling in the Molcas/OpenMolcas package. This implementation is applied to calculate relativistic hyperfine coupling (HFC) parameters for atomic systems and diatomic radicals with valence s or d orbitals by systematically varying active space size in the restricted active space self-consistent field formalism with restricted active space state interaction for spin–orbit coupling. The DKH relativistic treatment of the hyperfine interaction reduces the Fermi contact contribution to the HFC due to the presence of kinetic factors that regularize the singularity of the Dirac delta function in the nonrelativistic Fermi contact operator. This effect is more prominent for heavier nuclei. As the active space size increases, the relativistic correction of the Fermi contact contribution converges well to the experimental data for light and moderately heavy nuclei. The relativistic correction, however, does not significantly affect the spin-dipole contribution to the hyperfine interaction. In addition to the atomic and molecular systems, the implementation is applied to calculate the relativistic HFC parameters for large trivalent and divalent Tb-based single-molecule magnets (SMMs), such as Tb(III)Pc2 and Tb(II)(CpiPr5)2 without ligand truncation using well-converged basis sets. In particular, for the divalent SMM, which has an unpaired valence 6s/5d hybrid orbital, the relativistic treatment of HFC is crucial for a proper description of the Fermi contact contribution. Even with the relativistic hyperfine Hamiltonian, the divalent SMM is shown to exhibit strong tunability of HFC via an external electric field (i.e., strong hyperfine Stark effect).

Spin–spin interaction and magnetic Feshbach resonances in collisions of high-spin atoms with closed-shell atoms

We investigate interactions and ultracold collisions of high-spin but spherical atoms with closed-shell atoms, focusing on the example of Cr with Yb. Such a combination has only one potential energy curve but gives rise to a substantial intra-atomic spin–spin interaction, which causes Feshbach resonances due to rotationally excited states. We find such resonances are guaranteed below 250 G and can reach widths of tens of G in favorable circumstances. We study the effect of hyperfine structure, which can create additional wide resonances at low fields. Finally, we consider isotopic substitution and show that for any realistic potential it is very likely that at least one combination of commonly used isotopes will have resonances with experimentally favorable properties. Thus, this is a promising system for both molecule formation and studying quantum mixtures including dipolar species. Published by the American Physical Society 2024

Accurate hyperfine tensors for solid state quantum applications: case of the NV center in diamond

The decoherence of point defect qubits is often governed by the electron spin-nuclear spin hyperfine interaction that can be parameterized by using ab inito calculations in principle. So far most of the theoretical works have focused on the hyperfine interaction of the closest nuclear spins, while the accuracy of the predictions for distinct nuclear spins is barely discussed. Here we demonstrate for the case of the NV center in diamond that the absolute relative error of the computed hyperfine parameters can exceed 100% using an industry standards first-principles code. To overcome this issue, we implement an alternative method and report on significantly improved hyperfine values with O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{{{{{\\mathcal{O}}}}}}}}$$\\end{document}(1%) relative mean error at all distances. The provided accurate hyperfine data for the NV center enables high-precision simulation of NV quantum nodes for quantum information processing and positioning of nuclear spins by comparing experimental and theoretical hyperfine data.

Embracing disorder in quantum materials design

Many of the most exciting materials discoveries in fundamental condensed matter physics are made in systems hosting some degree of intrinsic disorder. While disorder has historically been regarded as something to be avoided in materials design, it is often of central importance to correlated and quantum materials. This is largely driven by the conceptual and theoretical ease to handle, predict, and understand highly uniform systems that exhibit complex interactions, symmetries, and band structures. In this Perspective, we highlight how flipping this paradigm has enabled exciting possibilities in the emerging field of high entropy materials, focusing primarily on high entropy oxide and chalcogenide quantum materials. These materials host high levels of cation or anion compositional disorder while maintaining unexpectedly uniform single crystal lattices. The diversity of atomic scale interactions of spin, charge, orbital, and lattice degrees of freedom are found to emerge into coherent properties on much larger length scales. Thus, altering the variance and magnitudes of the atomic scale properties through elemental selection can open new routes to tune global correlated phases, such as magnetism, metal–insulator transitions, ferroelectricity, and even emergent topological responses. The strategy of embracing disorder in this way provides a much broader pallet from which functional states can be designed for next-generation microelectronic and quantum information systems.

Plasmonically engineered nitrogen-vacancy spin readout.

Ultra-precise readout of single nitrogen-vacancy (NV) spins holds promise for major advancements in quantum sensing, computing, and communication technologies. Here we present a rigorous open quantum theory capable of simultaneously capturing the optical, vibronic, and spin interactions of the negatively charged NV center, both in the presence and absence of plasmonic interaction. Our theory is verified against existing experiments in the literature. We predict orders of magnitude brightness and contrast enhancements in optically detected magnetic resonance (ODMR) and NV spin qubit readout arising from plasmonic interaction. Such optimal enhancements occur in carefully engineered parameter regions, necessitating rigorous modelling prior to experimentation. Our theory equips the community with a tool to identify such regions.

Anisotropic relaxation of nuclear spins dipolar energy of water molecules in two-dimensional nanopores - A single crystal NMR study

Energy transfer from Zeeman to dipolar order discovered by Jeener et al. is usually observed in solids with a strong dipole-dipole interaction of nuclear spins. It is not observed in liquids, where fast molecular motion completely averages this interaction. The intermediate case, when the dipole-dipole interaction of nuclear spins is only partially averaged, has been poorly studied. We report on the first measurement of an angular-dependent proton spin relaxation of a dipolar reservoir in mobile water molecules confined in the interlayer pores of a vermiculite single crystal. In this layered crystal, the intramolecular dipole-dipole interactions of nuclear spins are only partially averaged due to the restricted anisotropic molecular motion in nanopores. We show that this allows the formation of dipolar echo. We measured the spin-lattice relaxation times of the dipolar order T1D at different angles between the normal to the crystal surface and the applied magnetic field and obtained a distinct angular dependence of T1D. The minimum relaxation rate R1D was found around the magic angle of 54.74°.

On the “contact” hyperfine interaction

When Enrico Fermi analyzed the magnetic interaction between the electron and Na, Cs, and Rb nuclei in 1930, he used the Dirac equation to compute the energy of an electron interacting with a point charge and magnetic dipole (the nucleus) fixed at the origin. After the mathematical dust had settled, he found an interaction that appeared to act only at a single point: the center of the electron wavefunction; it has been called a contact interaction. In 1936, Casimir analyzed the magnetic interaction of proton and neutron spins in the ground state of the deuteron using the Schrödinger equation and classical electrodynamics. Using symmetries appropriate only to s states, and performing an integration by parts, he found that they, too, seemed to interact only at a single common point of the proton and neutron: their center-of-mass. When applied to hydrogen, his result agreed with Fermi's. We present an expanded version of Casimir's important but little-known calculation.

Synthesis, disorder and Ising anisotropy in a new spin liquid candidate PrMgAl11O19

Here we report the successful synthesis of large single crystals of triangular frustrated PrMgAl11O19 using the optical floating zone technique. Single crystal x-ray diffraction (XRD) measurements unveiled the presence of quenched disorder within the mirror plane, specifically ~7% of Pr ions deviating from the ideal 2d site towards the 6h site. Magnetic susceptibility measurements revealed an Ising anisotropy with the c-axis being the easy axis. Despite a large spin–spin interaction that develops below ~10 K and considerable site disorder, the spins do not order or freeze down to at least 50 mK. The availability of large single crystals offers a distinct opportunity to investigate the exotic magnetic state on a triangular lattice with an easy axis out of the plane.

Morphology, physical, and structural aspects of copper nanoparticles induced- metal phosphate nanocompounds for gamma ray shielding and magnetic sensing applications

The inorganic nanocompounds were synthesized by solid state reaction with the composition 10Li2O+(30-x)Sb2O3 + xZnO + 59.5P2O5 + 0.5Cu (in mol%). SEM morphographs of the samples confirmed the grain size ≈0.5–2.5 μm. The EDAX spectra of the samples confirmed presence of copper (Cu) nanoparticles (<2 wt%) in the composition. The EDAX studies showed energy dispersion of Kα- photons by reactivity of elements P, Cu, and Zn, while the element Sb has shown dispersion of Lα- photons up to 10 keV. Mass attenuation coefficient (MAC) has exhibited a few discontinuities (bumps) at low energies (<10 keV) due to K, L- absorption edges of various elements (such as P, Cu, Zn, and Sb) presented in the samples. The shrinking of Phosphorous-Phosphorous separation (dP-P) from 4.716 Ao to 3.990 Ao indicated the greater solidity (or density) of the prepared nanocompounds at higher content of ZnO. XRD spectra showed the presence of major crystallites such as LiPO3, Li3PO4, Li6P6018, SbPO4, Cu3PO4, Cu2P2O7, Cu3[PO4]2, Zn[PO3]2, Zn2P2O7, ZnP4O11, and LiZnPO4 in the prepared nanocompounds. The average crystallite size was determined in the range of 35–83 nm. FTIR spectra of these compounds displayed the [PO2]−, [PO3]−, [PO4]3−, and [ZnO4] units along with linkages P─O─P, O─P─O, Sb─O─Sb, Cu─O─Cu, etc. A band due to vibrations of Cu─O bond has been observed in the range of 466–478 cm−1, which endorses the contribution of copper nanoparticles in the solid state reaction of the metal phosphate nanocompounds. A partially resolved hyperfine structure of magnetic resonance signals corresponding to g|| ≈2.4 and g⊥ ≈2.05 were observed due to the presence of an anisotropic hyperfine interaction of the electron spin (S = 1/2) with the nuclear spin (I = 3/2) of copper isotopes (63Cu and 65Cu) in the samples.

Unraveling the Nature of Spin Coupling in a Metal-Free Diradical: Theoretical Distinction of Ferromagnetic and Antiferromagnetic Interactions.

Metal-free diradicals based on polycyclic aromatic hydrocarbons are promising candidates for organic spintronics due to their stable magnetism and tunable spin coupling. However, distinguishing and elucidating the origins of ferromagnetic and antiferromagnetic interactions in these systems remain challenging. Here, we investigate the 2-OS diradical molecule sandwiched between gold electrodes using a combined density functional theory and hierarchical equations of motion approach. We find that the dihedral angle between the radical moieties controls the nature and strength of the intramolecular spin coupling, transitioning smoothly from antiferromagnetic to ferromagnetic as the angle increases. Distinct features in the inelastic electron tunneling spectra are identified that can discern the two coupling regimes, including spin excitation steps whose energies directly reveal the exchange coupling constant. Mechanical stretching of the junction is predicted to modulate the spectral line shapes by adjusting the hybridization of the molecular radicals with the electrodes. Our work elucidates the electronic origin of tunable spin interactions in 2-OS and provides spectroscopic fingerprints for characterizing magnetism in metal-free diradicals.

Changing the order of a dynamical phase transition through fluctuations in a quantum p-spin model

We study the non-equilibrium phase diagram of a fully-connected Ising p-spin model, for generic p > 2, and investigate its robustness with respect to the inclusion of spin-wave fluctuations, resulting from a ferromagnetic, short-range spin interaction. In particular, we investigate the dynamics of the mean-field model after a quantum quench: we observe a new dynamical phase transition which is either first or second order depending on the even or odd parity of p, in stark contrast with its thermal counterpart which is first order for all p. The dynamical phase diagram is qualitatively modified by the fluctuations introduced by a short-range interaction which drive the system always towards various prethermal paramagnetic phases determined by the strength of time dependent fluctuations of the magnetization.

Spin interaction of nonrelativistic neutrons with an ultrashort laser pulse

The nonrelativistic Pauli equation is used to study the interaction of slow neutrons with an ultrashort laser pulse. In the extreme limit, the pulse is acting on the magnetic moment of the neutron only at one instant of time. We obtain the scattering amplitude by deriving the junction conditions for the Pauli wave function across the pulse. Explicit expressions are given for a beam of polarized plane wave neutrons subjected to a pulse of spatially constant magnetic field strength. Finally we provide crude numerical estimates for pulses with the highest intensity available today.

Steric Control of Luminescence in Phenyl-Substituted Trityl Radicals.

Triphenylmethyl (trityl) radicals have shown potential for use in organic optoelectronic applications, but the design of practical trityl structures has been limited to donor/radical charge-transfer systems due to the poor luminescence of alternant symmetry hydrocarbons. Here, we circumvent the symmetry-forbidden transition of alternant hydrocarbons via excited-state symmetry breaking in a series of phenyl-substituted tris(2,4,6-trichlorophenyl)methyl (TTM) radicals. We show that 3-fold phenyl substitution enhances the emission of the TTM radical and that steric control modulates the optical properties in these systems. Simple ortho-methylphenyl substitution boosts the photoluminescence quantum efficiency from 1% (for TTM) to 65% at a peak wavelength of 612 nm (for 2-T3TTM) in solution. In the crystalline solid state, the neat 2-T3TTM radical shows a remarkably high photoluminescence quantum efficiency of 25% for emission peaking at 706 nm. This has implications in the design of aryl-substituted radical structures where the electronic coupling of the substituents influences variables such as emission, charge transfer, and spin interaction.