Nuclear Spin-spin Interactions Research Articles

Simulation of hyperfine-rotational spectrum of electromagnetic dipole transition rotation of BrF molecules

The transition dipole of the hyperfine-rotation spectrum of <i>J</i> = 1←0 within the vibronic ground (X<sup>1</sup>Σ, <i>v</i> = 0) state of BrF molecule is derived, and thus, the transition selection rules are summarized as follows: Δ<i>J =</i> ±1; Δ<i>F</i><sub>1</sub> = 0, ±1 and Δ<i>F </i>= 0, ±1, and those of Δ<i>F</i><sub>1</sub> = Δ<i>F</i> are intense while those of Δ<i>F</i><sub>1</sub> ≠ Δ<i>F</i> are weak. Some spectral lines result from both the electric dipole transition and nuclear magnetic dipole transition due to perturbations, however, the magnetic dipole transition only contributes about one-billionth in the spectral intensity. The spectral linewidth is determined to be about 18 kHz by calculating the spectral transition probability. The obtained spectral linewidth and relative intensities are consistent with the experimental results. Additionally, the hyperfine-rotation spectral positions are determined by diagonalizing the Hamiltonian matrix in the basis of |<i>JI</i><sub>1</sub><i>F</i><sub>1</sub><i>I</i><sub>2</sub><i>F</i><inline-formula><tex-math id="Z-20230210104836">\begin{document}$\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221957_Z-20230210104836.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221957_Z-20230210104836.png"/></alternatives></inline-formula>, which is also in good agreement with the experiments within 10<sup>–8</sup> (one-fiftieth of the spectral line width). Hence, the microwave hyperfine-rotation spectrum is simulated. In addition, we find that the nuclear spin-spin interaction not only slightly shifts the hyperfine-rotation spectral positions but also changes the sequence of the spectra. As to those unavailable constants of molecules, the fairly precise molecular constants can be achieved by quantum chemical calculation, say, by employing MOLPRO program, and then the simulated spectra can guide the spectral assignment. Besides the guidance of spectral assignment, our results are also helpful for other relevant applications such as in absolute single quantum state preparation.

Freezing of the Lattice in the Kagome Lattice Heisenberg Antiferromagnet Zn-Barlowite ZnCu_{3}(OD)_{6}FBr.

We use ^{79}Br nuclear quadrupole resonance (NQR) to demonstrate that ultraslow lattice dynamics set in below the temperature scale set by the Cu-Cu superexchange interaction J (≃160 K) in the kagome lattice Heisenberg antiferromagnet Zn-barlowite. The lattice completely freezes below 50K, and ^{79}Br NQR line shapes become twice broader due to increased lattice distortions. Moreover, the frozen lattice exhibits an oscillatory component in the transverse spin echo decay, a typical signature of pairing of nuclear spins by indirect nuclear spin-spin interaction. This indicates that some Br sites form structural dimers via a pair of kagome Cu sites prior to the gradual emergence of spin singlets below ∼30 K. Our findings underscore the significant roles played by subtle structural distortions in determining the nature of the disordered magnetic ground state of the kagome lattice.

Scalable nuclear-spin entanglement mediated by a mechanical oscillator

We propose a solid-state hybrid platform based on an array of implanted nitrogen-vacancy (NV) centers in diamond magnetically coupled to a mechanical oscillator. The mechanical oscillator and the NV electronic spins both act as a quantum bus and allow us to induce an effective long-range interaction between distant nuclear spins, relaxing the requirements on their spatial distance. The coherent nuclear spin-spin interaction, having the form of an Ising model, can be maintained in the presence of mechanical damping and spin dephasing via a pulsed dynamical decoupling of the nuclear spins in addition to the microwave driving field of the electronic spins. The present hybrid platform provides a scalable way to prepare multipartite entanglement among nuclear spins with long coherence times and can be applied to generate graph states that may be used for universal quantum computing.

Effects of nuclear spins on the transport properties of the edge of two-dimensional topological insulators

The electrons in the edge channels of two-dimensional topological insulators can be described as a helical Tomonaga-Luttinger liquid. They couple to nuclear spins embedded in the host materials through the hyperfine interaction, and are therefore subject to elastic spin-flip backscattering on the nuclear spins. We investigate the nuclear-spin-induced edge resistance due to such backscattering by performing a renormalization-group analysis. Remarkably, the effect of this backscattering mechanism is stronger in a helical edge than in nonhelical channels, which are believed to be present in the trivial regime of InAs/GaSb quantum wells. In a system with sufficiently long edges, the disordered nuclear spins lead to an edge resistance which grows exponentially upon lowering the temperature. On the other hand, electrons from the edge states mediate an anisotropic Ruderman-Kittel-Kasuya-Yosida nuclear spin-spin interaction, which induces a spiral nuclear spin order below the transition temperature. We discuss the features of the spiral order, as well as its experimental signatures. In the ordered phase, we identify two backscattering mechanisms, due to charge impurities and magnons. The backscattering on charge impurities is allowed by the internally generated magnetic field, and leads to an Anderson-type localization of the edge states. The magnon-mediated backscattering results in a power-law resistance, which is suppressed at zero temperature. Overall, we find that in a sufficiently long edge the nuclear spins, whether ordered or not, suppress the edge conductance to zero as the temperature approaches zero.

Solid-State NMR Structural Characterization of Self-Assembled Peptides with Selective 13C and 15N Isotopic Labels.

For the structural characterization methods discussed here, information on molecular conformation and intermolecular organization within nanostructured peptide assemblies is discerned through analysis of solid-state NMR spectral features. This chapter reviews general NMR methodologies, requirements for sample preparation, and specific descriptions of key experiments. An attempt is made to explain choices of solid-state NMR experiments and interpretation of results in a way that is approachable to a nonspecialist. Measurements are designed to determine precise NMR peak positions and line widths, which are correlated with secondary structures, and probe nuclear spin-spin interactions that report on three-dimensional organization of atoms. The formulation of molecular structural models requires rationalization of data sets obtained from multiple NMR experiments on samples with carefully chosen 13C and 15N isotopic labels. The information content of solid-state NMR data has been illustrated mostly through the use of simulated data sets and references to recent structural work on amyloid fibril-forming peptides and designer self-assembling peptides.

Measurement of untruncated nuclear spin interactions via zero- to ultralow-field nuclear magnetic resonance

Zero- to ultra-low-field nuclear magnetic resonance (ZULF NMR) provides a new regime for the measurement of nuclear spin-spin interactions free from effects of large magnetic fields, such as truncation of terms that do not commute with the Zeeman Hamiltonian. One such interaction, the magnetic dipole-dipole coupling, is a valuable source of spatial information in NMR, though many terms are unobservable in high-field NMR, and the coupling averages to zero under isotropic molecular tumbling. Under partial alignment, this information is retained in the form of so-called residual dipolar couplings. We report zero- to ultra-low-field NMR measurements of residual dipolar couplings in acetonitrile-2-$^{13}$C aligned in stretched polyvinyl acetate gels. This represents the first investigation of dipolar couplings as a perturbation on the indirect spin-spin $J$-coupling in the absence of an applied magnetic field. As a consequence of working at zero magnetic field, we observe terms of the dipole-dipole coupling Hamiltonian that are invisible in conventional high-field NMR. This technique expands the capabilities of zero- to ultra-low-field NMR and has potential applications in precision measurement of subtle physical interactions, chemical analysis, and characterization of local mesoscale structure in materials.

Dynamics of a mesoscopic nuclear spin ensemble interacting with an optically driven electron spin

The ability to discriminate between simultaneously occurring noise sources in the local environment of semiconductor InGaAs quantum dots, such as electric and magnetic field fluctuations, is key to understanding their respective dynamics and their effect on quantum dot coherence properties. We present a discriminatory approach to all-optical sensing based on two-color resonance fluorescence of a quantum dot charged with a single electron. Our measurements show that local magnetic field fluctuations due to nuclear spins in the absence of an external magnetic field are described by two correlation times, both in the microsecond regime. The nuclear spin bath dynamics show a strong dependence on the strength of resonant probing, with correlation times increasing by a factor of four as the optical transition is saturated. We interpret the behavior as motional averaging of both the Knight field of the resident electron spin and the hyperfine-mediated nuclear spin-spin interaction due to optically-induced electron spin flips.

Electron and nuclear spin dynamics in plastically deformed silicon crystals enriched in isotope 29Si

Paramagnetic defects of a new type with a concentration of about 1015 cm−3 are shown to be generated during the plastic deformation of isotope-rich (72%, 76% 29Si) silicon crystals at a temperature of 950°C. The electron paramagnetic resonance (EPR) spectra of these defects are anisotropic and have a significant width (up to 1 kOe). The nonuniform broadening of the EPR lines is caused by the variation of the internal magnetic field in correlated defect clusters. The nuclear magnetic resonance (NMR) spectra of the deformed crystals consist of Pake doublets split by nuclear spin-spin interaction. The broadening of the NMR spectra is caused by nuclear dipole-dipole relaxation.

Understanding multi-quantum NMR through secular approximation

With the development of technology and improved understanding of nuclear spin-spin interactions and their behavior in static/oscillating magnetic fields, NMR spectroscopy has emerged as a powerful tool for characterizing molecular structure in a wide range of systems of chemical, physical and biological relevance. Here in this article, we revisit the important connection between "Secular-Approximation" (a well-known fundamental concept) and NMR spectroscopy. Employing recent experimental results as the background, an alternate interpretation of the secular approximation is presented for describing and understanding the nuances of Multi-Quantum (MQ) NMR spectroscopy of quadrupolar nuclei. Since MQ NMR spectroscopy of quadrupolar nuclei forms the basis of the structural characterization of inorganic solids and clusters, we believe that the analytic theory presented herein would be beneficial both in the understanding and design of MQ NMR experiments. Additionally, the analytic results are corroborated with rigorous numerical simulations and could be employed in the quantitative interpretation of experimental results.

Spin–Spin Interactions and Nuclear Magnetic Relaxation in Magnetic Solids

The influence of the orientational fluctuations of the electronic magnetization, which modulate nuclear spin-spin interactions (Suhl-Nakamura and dipole-dipole), on the spin-lattice relaxation of magnetic nuclei with spin I = 1/2 in the magnetically ordered solids has been investigated. It has been shown that this mechanism of the spin-lattice relaxation is less effective in comparison with the process of spin-lattice relaxation caused by the direct fluctuations of hyperfine fields, which appear when there are the fluctuations of electronic magnetization direction.

Theoretical model for enrichment ofCH3Fnuclear-spin isomers by resonant microwave radiation

Theoretical model of the coherent control of nuclear spin isomers by microwave radiation has been developed. Model accounts the M-degeneracy of molecular states and molecular center-of-mass motion. The model has been applied to the 13CH3F molecules. Microwave radiation excites the para state (J=11,K=1) which is mixed by the nuclear spin-spin interaction with the ortho state (9,3). Dependencies of the isomer enrichment and conversion rates on the radiation frequency have been calculated. Both spectra consist of two resonances situated at the centers of allowed and forbidden (by nuclear spin) transitions in the molecule. Larger enrichment, up to 7%, can be produced by strong radiation resonant to the forbidden transition. The spin conversion rate can be increased by 2 orders of magnitude at this resonance.

Widely usable interpolation formulae for hyperfine splittings in the 127I2 spectrum

Based on new systematic high precision measurements of hyperfine splittings in different rovibrational bands of 127I2 in the near infrared spectral range between 778 nm and 816 nm, and the data in the range from 660 nm to 514 nm available from literature, the quantum number dependence of the different hyperfine interaction parameters was reinvestigated. As detailed as possible parameters were re-fitted from the reported hyperfine splittings in literature, considering that the interaction parameters should vary smoothly with the vibrational and rotational quantum numbers, and follow appropriate physical models. This type of consistency has not been sufficiently taken into account by other authors. To our knowledge it is now possible for the first time to separate the hfs contributions of the two electronic states B 3Пo + u and X 1 Σ + for optical transitions in a very large wavelength range. New interpolation formulae could be derived for both states, describing the quantum number dependences of the nuclear electric quadrupole. of the nuclear spin-rotation and also of the nuclear spin-spin interactions. Using these new interpolation formulae the hyperfine splittings for the components with the quantum number condition F − J = 0 can be calculated with an uncertainty of ≤30 kHz for transitions in the wavelength range between 514 nm and 820 nm.

New ortho-para conversion mechanism in dense solid hydrogen.

Analysis of recent measurements of striking changes in the rate of ortho-para conversion of solid H(2) up to 58 GPa shows that the conversion mechanism must differ from that at ambient pressure. A new conversion mechanism is identified in which the emerging excitations are coupled to the converting molecules via electric quadrupole-quadrupole rather than nuclear spin-spin interactions. The latter only initiates conversion while the coupling enhancement associated with the new mechanism is ensured by high compression and a gap closing, with the conversion energy diminishing strongly with increasing pressure.

Nuclear-spin relaxation of59Cocorrelated with the spin-state transitions inLaCoO3

The ${}^{59}\mathrm{C}\mathrm{o}\ensuremath{-}\mathrm{N}\mathrm{M}\mathrm{R}$ on single crystals of ${\mathrm{LaCoO}}_{3}$ has been studied in order to investigate the spin-state transition through the nuclear-spin relaxation in this compound. Below $T\ensuremath{\sim}35\mathrm{K},$ the spin-lattice and spin-spin relaxation rates show a thermal-activation-type temperature dependence with an energy gap of \ensuremath{\sim}180 K. This value is close to the energy difference between the low spin state $(S=0)$ and the intermediate spin state $(S=1)$ predicted in the two-stage spin-state transition model with the intermediate spin state. The apparent spin-spin relaxation rates depend on the resonance peaks split due to the nuclear-electric-quadrupole interaction, which is explained by an indirect nuclear spin-spin interaction through the interacting paramagnetic electron spins. This observation is consistent with the ferromagnetic short-range correlation among the electron spins on ${\mathrm{Co}}^{3+}$ ions confirmed by neutron-scattering experiments.

Hyperfine spectra of CH3F nuclear spin conversion

A theoretical model of hyperfine spectra of nuclear spin conversion of molecular isomers has been developed. The model takes into account the nuclear spin-spin and spin-rotation interactions, as well as the saturation of intramolecular mixing of molecular ortho and para states. The model has been applied to hyperfine spectra of nuclear spin conversion in 13CH3F molecules subjected to an external electric field. Conditions under which the hyperfine structure in the spectra can be resolved have been determined.

Cu-NQR Study in the Paramagnetic State in YBa2Cu3O6

The NQR measurements for the Cu(2) and the Cu(1) sites in antiferromagnetic insulator YBa 2 Cu 3 O 6 with T N =415 K were carried out in the paramagnetic state for the respective temperature ranges of 475–575 K and of 295–775 K. For the Cu(2) sites, the nuclear spin-lattice relaxation rate 1/ T 1 and the second moment of the indirect nuclear spin-spin interactions 1/ T 2G exhibit a similar behavior to those in La 2 CuO 4 not only in the temperature dependence but also in the magnitude at least below 550 K. These results suggest a possibility that the renormalized classical description for two-dimensional quantum Heisenberg antiferromagnet is also applicable to YBa 2 Cu 3 O 6 as to La 2 CuO 4 and that the upper limit of the bilayer coupling J ''/ J is as large as 10 -2 , where J and J '' are the intra-layer and bilayer exchange couplings, respectively. The Cu(1) NQR does not probe any spin dynamics in the CuO 2 plane except for the temperatures below 600 K. The rapid increase in 1/ T 1 above 600 K suggests...

Indirect nuclear spin-spin interactions in PbTe

We make a careful analysis of various contributions to the indirect ${}^{207}\mathrm{Pb}$ nuclear spin-spin interactions ${A}_{{\mathrm{jj}}^{\ensuremath{'}}}$ in PbTe. The calculation takes into account all three hyperfine interactions and includes both the intraband and the interband contributions within a $\mathbf{k}\ensuremath{\cdot}\mathbf{\ensuremath{\pi}}$ formalism. The relativistic effects are considered through the double group basis wave functions and energy levels around the energy gap. We calculate ${A}_{{\mathrm{jj}}^{\ensuremath{'}}}$ from three different contributions: (a) a full valence band and an empty conduction band, (b) electrons in $n$-type PbTe, and (c) holes in $p$-type PbTe. In the first case the coupling tensor is quite appreciable and changes from ferromagnetic (FM) order to antiferromagnetic (AFM) order as the internuclear separation $R$ increases. In the case of full band contribution all of the hyperfine interactions are found to be important. The carrier contributions are calculated in each case for two typical carrier (both electron and hole) densities. In the case of $p$-type PbTe, ${A}_{{\mathrm{jj}}^{\ensuremath{'}}}$ is isotropic and due mainly to contact hyperfine interactions. The noncontact interactions arising out of mixing of bands, albeit weak, are also taken into account. In the case of $n$-type PbTe the noncontact hyperfine interactions, namely, the orbital and the dipolar interactions, are important and the coupling constant is anisotropic. The coupling constants calculated for carrier densities of the order of ${10}^{18} {\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ are found to be about four orders less than the corresponding value in metallic lead. Although there are no experimental results for comparison, the order of magnitude appears to be reasonable in view of the low density of carriers considered, as compared to the metallic density. Furthermore, in the absence of any other theoretical work in the case of semiconductors in general and in PbTe in particular, the present work furnishes valuable information regarding the nature of hyperfine interactions and their relative contributions to the indirect nuclear spin-spin interaction in PbTe. Some of the systematics of our calculation agree with those predicted in the case of indirect exchange interaction involving magnetic impurities in PbTe.

Adiabatic channel study of the capture of nitrogen and oxygen molecules by an ion: effect of nuclear symmetry and spin-spin interaction

Within the adiabatic channel treatment of ionmolecule capture we have calculated the low temperature capture rate constants of N2(1Σg+) and O2(3Σg−)in collisions with positive and negative ions. In both cases, the charge-quadrupole and the anisotropic charge-induced dipole interactions produce noticeable deviations from the Langevin rate constant. The rate constants calculated with account for the anisotropic interaction, in addition, are substantially affected by nuclear symmetry; in the case of O2(3Σg−), the fine-structure spin-spin interaction strongly manifests itself in the rate constants.

Specific heat below 1 mK and the electric-field gradient in indium.

The specific heat of polycrystalline indium has been measured to well below 1 mK to determine the nuclear quadrupole interaction and to study the nuclear spin-spin interaction. The sign of the electric field gradient eq is found to be positive instead of the negative sign reported previously. This sign agrees with a recent calculation based on band theory. The local field coming from the nuclear spin-spin interaction is determined to be ${\mathit{b}}_{\mathrm{int}}$=43\ifmmode\pm\else\textpm\fi{}5 mT in indium. \textcopyright{} 1996 The American Physical Society.

63,65Cu and 17O spin-echo decay and the static susceptibility chi '(q) in La1.85Sr0.15CuO4.

Data are presented and analyzed for the nuclear spin-echo decay of $^{63,65}\mathrm{Cu}$ and $^{17}\mathrm{O}$ in ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ at T=100 K. The echo-decay data are compared with calculated waveforms in which time fluctuations of coupled neighbor spins are taken into account. Data for the two copper isotopes are found to show the effects of both ${\mathit{T}}_{1}$ and nuclear spin exchange fluctuations. Experimental decay rates for the $^{63,65}\mathrm{Cu}$ are in good agreement with indirect nuclear spin-spin interactions calculated using values of \ensuremath{\chi}'(q,0) inferred from neutron-scattering data for S(q,\ensuremath{\omega}) for this system. For $^{17}\mathrm{O}$, the echo decay is found to be in good agreement with an interpretation based on Cu-O nuclear dipolar couplings alone, in which the same Cu ${\mathit{T}}_{1}$ and nuclear spin exchange values are employed as for the copper echo decay. Calculated Cu-O indirect couplings of comparable magnitude to the dipole-dipole terms are therefore concluded to be absent. We further conclude that the transferred Cu-O hyperfine coupling is much smaller than that deduced from the measured $^{17}\mathrm{O}$ NMR shift. It follows that the excitations which provide the $^{17}\mathrm{O}$ NMR shift and relaxation are separate and distinct from those associated with spin fluctuations on the copper sites. Similar conclusions were reached in a recent study of $^{17}\mathrm{O}$ nuclear spin-lattice relaxation in this system.