Effective Hyperfine Research Articles

Observation of dynamic nuclear polarization echoes.

It is demonstrated that the time evolution of the electron-nuclear polarization transfer process during pulsed dynamic nuclear polarization (DNP) can be reversed on a microsecond timescale, leading to the observation of DNP echoes. The DNP echoes are induced by consecutive application of two pulse trains that produce effective Hamiltonians that differ only in the sign of the effective hyperfine coupling. The experiments have been performed on a frozen solution of trityl radicals in water/glycerol on a homebuilt X-band electron paramagnetic resonance/DNP spectrometer at 80 kelvins. We envisage that DNP echoes will play an important role in future development of pulsed DNP for sensitivity-enhanced nuclear magnetic resonance, hyperfine spectroscopy, and quantum sensing.

Metal-carbon bonding in early lanthanide substituted cyclopentadienyl complexes probed by pulsed EPR spectroscopy.

We examine lanthanide (Ln)-ligand bonding in a family of early Ln3+ complexes [Ln(Cptt)3] (1-Ln, Ln = La, Ce, Nd, Sm; Cptt = C5H3tBu2-1,3) by pulsed electron paramagnetic resonance (EPR) methods, and provide the first characterization of 1-La and 1-Nd by single crystal XRD, multinuclear NMR, IR and UV/Vis/NIR spectroscopy. We measure electron spin T1 and Tm relaxation times of 12 and 0.2 μs (1-Nd), 89 and 1 μs (1-Ce) and 150 and 1.7 μs (1-Sm), respectively, at 5 K: the T1 relaxation of 1-Nd is more than 102 times faster than its valence isoelectronic uranium analogue. 13C and 1H hyperfine sublevel correlation (HYSCORE) spectroscopy reveals that the extent of covalency is negligible in these Ln compounds, with much smaller hyperfine interactions than observed for equivalent actinide (Th and U) complexes. This is corroborated by ab initio calculations, confirming the predominant electrostatic nature of the metal-ligand bonding in these complexes.

A hyperfine-resolved spectroscopic model for vanadium monoxide (51V16O)

Vanadium monoxide ( 51 V 16 O) is believed to play an important role in the atmospheres of hot-Jupiters, but high-resolution studies have so far failed to detect it, at least in part because of the inaccuracy of available lists. It is likely that the large hyperfine splittings in the spectra of VO, arising from the large nuclear spin I = 7 2 of the 51 V atom, has contributed to the non-detections with the current hyperfine-unresolved VOMYT line list. To aid in the production of a new line list, a fully hyperfine-resolved spectroscopic model has been constructed which includes 15 low-lying electronic states (6 quartets and 9 doublets) of VO with the inclusion of hyperfine couplings based on use of the new, hyperfine-resolved version of the diatomic variational nuclear motion programme Duo. The new spectroscopic model is refined against empirical Marvel energies derived from experimental transitions, and hyperfine couplings are fit for the 3 electronic states for which hyperfine effects have been resolved in lab spectra. This model is used to assign some previously identified perturbations.

Sublattice spin reversal and field induced Fe3+ spin-canting across the magnetic compensation temperature in Y1.5Gd1.5Fe5O12 rare-earth iron garnet

In the present work Fe3+ sublattice spin reversal and Fe3+ spin-canting across the magnetic compensation temperature (T) are demonstrated in polycrystalline Y1.5Gd1.5Fe5O12 (YGdIG) by means of in-field Mössbauer spectroscopy measurements. Corroborating in-field Mössbauer measurements, both Fe3+ & Gd3+ sublattice spin reversal has also been manifested in hard x-ray magnetic circular dichroism (XMCD) measurements. From in-field 57 Fe Mössbauer measurements, estimation and analysis of effective internal hyperfine field (H), relative intensity of absorption lines in a sextet elucidated unambiguously the signatures of Fe3+ spin reversal and field induced spin-canting of Fe3+ sublattices across T. Gd L3-edge XMCD signal is observed to consist of an additional spectral feature, identified as Fe3+ magnetic contribution to XMCD spectra of Gd L3-edge, enabling us the extraction of both the sublattices (Fe3+ & Gd3+) information from a single absorption edge analysis. The evolution of the XMCD amplitudes, which is proportional to magnetic moments, as a function of temperature for both magnetic sublattices extracted at the Gd L3-edge reasonably match with values that are extracted from bulk magnetization data of YGdIG and YIG (Y3Fe5O12) and corresponding Fe K-edge XMCD amplitudes for Fe contribution. These measurements pave new avenues to investigate how the magnetic behavior of such complex system acts across the compensation point.

Electron-nuclear decoupling at a spin clock transition

The ability to design quantum systems that decouple from environmental noise sources is highly desirable for development of quantum technologies with optimal coherence. The chemical tunability of electronic states in magnetic molecules combined with advanced electron spin resonance techniques provides excellent opportunities to address this problem. Indeed, so-called clock transitions have been shown to protect molecular spin qubits from magnetic noise, giving rise to significantly enhanced coherence. Here we conduct a spectroscopic and computational investigation of this physics, focusing on the role of the nuclear bath. Away from the clock transition, linear coupling to the nuclear degrees of freedom causes a modulation and decay of electronic coherence, as quantified via electron spin echo signals generated experimentally and in silico. Meanwhile, the effective hyperfine interaction vanishes at the clock transition, resulting in electron-nuclear decoupling and an absence of quantum information leakage to the nuclear bath, providing opportunities to characterize other decoherence sources.

Hyperfine effects and electron spin relaxation of 51V4+ doped into scandium orthosilicate Sc228SiO5: CW and pulsed X-band electron spin resonance studies

Hyperfine effects and electron spin relaxation of 51V4+ doped into scandium orthosilicate Sc228SiO5: CW and pulsed X-band electron spin resonance studies

An empirical spectroscopic model for eleven electronic states of VO

Previously-determined empirical energy levels are used to construct a rovibronic model for the X4Σ−, A′4Φ, A4Π, B4Π, C4Σ−, D4Δ, 12Δ, 12Σ+, 12Φ, 12Π and 22Π electronic states of vanadium monoxide. The spectrum of VO is characterized by many couplings and crossings between the states associated with these curves. The model is based on the use of potential energy curves, represented as extended Morse oscillators, and couplings (spin–orbit, spin–spin, angular momentum), represented by polynomials, which are tuned to the data plus an empirical allowance for spin–rotation couplings. The curves are used as input for the variational nuclear motion code Duo. For the X4Σ−, 12Φ and 12Π states the model reproduces the observed energy to significantly better than 0.1 cm−1. For the other states the standard deviations are between 0.25 and 1.5 cm−1. Further experimental data and consideration of hyperfine effects would probably be needed to significantly improve this situation.

Intensities of KCs [formula omitted] band system up to dissociation threshold: an interplay between spin-orbit, hyperfine and rovibronic coupling effects

The relative intensity distribution in the rotationally resolved laser-induced fluorescence spectra belonging to the E(4)1Σ+→(a3Σ1+,X1Σ+) band systems of the KCs molecule was analyzed. The experimental intensities in doublet P,R progressions assigned to spin-allowed E→X and spin-forbidden E→a transitions up to their common ground dissociation limit were described in the framework of a coupled-channels (CC) deperturbation model applied for the interacting X1Σ+ and a3Σ+ states. The CC intensity simulation was based solely on fixed electronic structure parameters as functions of the internuclear distance R, namely: accurate empirical potential energy curves for all three states, ab initio estimates for matrix elements A(R) of the hyperfine structure (HFS), and transition dipole moments dEX(R) and dEa(R). A comparison between the measured intensities and their theoretical counterparts demonstrates a strong competition between different intramolecular interactions. A weak spin-orbit coupling of the upper E(4)1Σ+ state with the remote 3Π states is responsible for appearance of the E→a vibrational bands for the intermediate va-values. In turn, the HFS coupling between X1Σ+ and a3Σ+ states leads to peculiarities in E→(X,a) intensities, which are pronounced for high vX/a-values in the vicinity of K(42S)+Cs(62S) dissociation threshold. Both adiabatic ro-vibrational and non-adiabatic electronic-rotational interactions explain the abrupt deviation of some observed P/R intensity ratios from the expected Hönl-London factors.

The nuclear-spin-forbidden rovibrational transitions of water from first principles.

The water molecule occurs in two nuclear-spin isomers that differ by the value of the total nuclear spin of the hydrogen atoms, i.e., I = 0 for para-H2O and I = 1 for ortho-H2O. Spectroscopic transitions between rovibrational states of ortho and para water are extremely weak due to the tiny hyperfine nuclear-spin-rotation interaction of only ∼30 kHz and, so far, have not been observed. We report the first comprehensive theoretical investigation of the hyperfine effects and ortho-para transitions in H2 16O due to nuclear-spin-rotation and spin-spin interactions. We also present the details of our newly developed general variational approach to the simulation of hyperfine effects in polyatomic molecules. Our results for water suggest that the strongest ortho-para transitions with room-temperature intensities on the order of 10-31 cm/molecule are about an order of magnitude larger than previously predicted values and should be detectable in the mid-infrared ν2 and near-infrared 2ν1 + ν2 and ν1 + ν2 + ν3 bands by current spectroscopy experiments.

Comparison of Lanthanide Macrocyclic Complexes as 23Na NMR Sensors.

Nuclear magnetic resonance (NMR) agents, composed of paramagnetic lanthanide ions (Ln3+) complexed with negatively charged cyclic chelating agents (Che(n+3)-) forming polyanionic lanthanide complexes (LnChen-), perturb sodium-23 (23Na) signals, a phenomenon which depends sodium ions (Na+) exchanging with LnChen-. We analyzed 23Na shiftability and broadening due to hyperfine and bulk magnetic susceptibility (BMS) effects that arise from LnChen- designs using selective Ln3+ ions (i.e., thulium, Tm3+; gadolinium, Gd3+; and europium, Eu3+) and macrocyclics derived from 1,4,7,10-tetraazacyclododecane (cyclen) [i.e., with phosphonate (DOTP8-) and carboxylate (DOTMA4-) arms] and 1,4,7-triazacyclononane (TACN) [i.e., with phosphonate (NOTP6-) arms]. All LnChen- complexes showed downfield shifts, but Gd3+ and Tm3+ agents, respectively, were dominated by BMS and hyperfine effects, in good agreement with theory. While 23Na shiftability and broadening were minimally affected by pH and competing cations (K+, Ca2+, and Mg2+) within physiological ranges, the 23Na shiftability and broadening were most sensitive to LnChen- concentration in relation to the interstitial Na+ level in vivo. Greatest 23Na shiftability and broadening were obtained with Tm3+ and Gd3+ agents, respectively. While BMS contribution to shiftability was most impacted by the number of unpaired electrons on Ln3+, negative charge on LnChen- regulated Na+ exchange for line broadening. In brain tumor models, TmDOTP5- with 23Na-NMR has been used previously to separate Na+ in intracellular, blood, and interstitial pools, while evidence here shows that GdDOTP5- can distinguish Na+ within intracellular and extracellular (i.e., blood and interstitial) pools. Given the biological importance of Na+ in vivo, future macrocyclic designs of LnChen- should be sought for 23Na-NMR biomedical applications.

Coherent Spin Dynamics of Electrons and Holes in CsPbBr3 Colloidal Nanocrystals.

The spin dynamics in CsPbBr3 lead halide perovskite nanocrystals are studied by picosecond pump-probe Faraday rotation in an external magnetic field. Coherent Larmor precession of electrons and holes with spin dephasing times of ∼600 ps is detected in a transversal magnetic field. The longitudinal spin relaxation time in weak magnetic fields reaches 80 ns at a temperature of 5 K. In this regime, the carrier spin dynamics is governed by nuclear spin fluctuations characterized by an effective hyperfine field strength of 25 mT. The Landé factors determining the carrier Zeeman splittings are ge = +1.73 for electrons and gh = +0.83 for holes. A comparison with a CsPbBr3 polycrystalline film and bulk single crystals evidences that the spatial confinement of electrons and holes in the nanocrystals only slightly affects their g factors and spin dynamics.

Hyperfine-Resolved Near-Infrared Spectra of H217O.

Huge efforts have recently been taken in the derivation of accurate compilations of rovibrational energies of water, one of the most important reference systems in spectroscopy. Such precision is desirable for all water isotopologues, although their investigation is challenged by hyperfine effects in their spectra. Frequency-comb locked noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS) allows for achieving high sensitivity, resolution, and accuracy. This technique has been employed to resolve the subtle hyperfine splittings of rovibrational transitions of H217O in the near-infrared region. Simulation and interpretation of the H217O saturation spectra have been supported by coupled-cluster calculations performed with large basis sets and accounting for high-level corrections. Experimental 17O hyperfine parameters are found in excellent agreement with the corresponding computed values. The need of including small hyperfine effects in the analysis of H217O spectra has been demonstrated together with the ability of the computational strategy employed for providing quantitative predictions of the corresponding parameters.

Hyperfine structure of transition metal defects in SiC

Transition metal (TM) defects in silicon carbide (SiC) are a promising platform in quantum technology, especially because some TM defects emit in the telecom band. We develop a theory for the interaction of an active electron in the $D$-shell of a TM defect in SiC with the TM nuclear spin and derive the effective hyperfine tensor within the Kramers doublets formed by the spin-orbit coupling. Based on our theory we discuss the possibility to exchange the nuclear and electron states with potential applications for nuclear spin manipulation and long-lived nunclear-spin based quantum memories.

Magnetic Friedel Oscillation at the Fe(001) Surface: Direct Observation by Atomic-Layer-Resolved Synchrotron Radiation ^{57}Fe Mössbauer Spectroscopy.

The surface magnetism of Fe(001) was studied in an atomic layer-by-layer fashion by using the insitu iron-57 probe layer method with a synchrotron Mössbauer source. The observed internal hyperfine field H_{int} exhibits a marked decrease at the surface and an oscillatory behavior with increasing depth in the individual upper four layers below the surface. The calculated layer-depth dependencies of the effective hyperfine field |H_{eff}|, isomer shift δ, and quadrupole shift 2ϵ agree well with the observed experimental parameters. These results provide the first experimental evidence for the magnetic Friedel oscillations, which penetrate several layers from the Fe(001) surface.

NQR and NMR spectra in the odd-parity multipole material CeCoSi

We theoretically study NQR and NMR spectra in the presence of odd-parity multipoles originating from staggered antiferromagnetic and antiferroquadrupole orderings. For the $f$-electron metal, CeCoSi, which is a candidate hosting odd-parity multipoles, we derive an effective hyperfine field acting on Co nucleus generated from electronic origin multipole moments at Ce ion under zero and nonzero magnetic fields. We elucidate that emergent odd-parity multipoles give rise to sublattice-dependent spectral splittings in NQR and NMR through the effective hyperfine coupling in the absence of the global inversion symmetry. We mainly examine behaviors of the NQR and NMR spectra in three odd-parity multipole ordered states: a $y$-type magnetic toroidal dipole order with a staggered $x$-type antiferromagnetic structure, an $xy$-type electric toroidal quadrupole order with a staggered $x^2-y^2$-type antiferroquadrupole structure, and a $z$-type electric dipole order with a staggered $3z^2-r^2$-type antiferroquadrupole structure. We show that different odd-parity multipole orders lead to different field-dependent spectral splittings in NMR, while only the $xy$-type electric toroidal quadrupole order exhibits the NQR spectral splitting. We also present possible sublattice-dependent spectral splittings for all the odd-parity multipole orders potentially activated in low-energy crystal-field levels, which will be useful to identify odd-parity order parameters in CeCoSi by NQR and NMR measurements.

Internal rotation and chlorine nuclear quadrupole coupling in 2-chloro-4-fluorotoluene explored by microwave spectroscopy and quantum chemistry.

2-Chloro-4-fluorotoluene was investigated using a combination of molecular jet Fourier transform microwave spectroscopy in the frequency range from 5 to 21GHz and quantum chemistry. The molecule experiences an internal rotation of the methyl group, which causes fine splittings of all rotational transitions into doublets with separation on the order of a few tens of kHz. In addition, hyperfine effects originating from the chlorine nuclear quadrupole moment coupling its nuclear spin to the end-over-end rotation of the molecule are observed. The torsional barrier was derived using both the rho and the combined-axis-method, giving a value of 462.5(41) cm-1. Accurate rotational constants and quadrupole coupling constants were determined for the 35Cl and 37Cl isotopologues and compared with Bailey's semi-experimental quantum chemical predictions. The gas phase molecular structure was deduced from the experimental rotational constants supplemented with those calculated by quantum chemistry at various levels of theory. The values of the methyl torsional barrier and chlorine nuclear quadrupole coupling constants were compared with the theoretical predictions and with those of other chlorotoluene derivatives.

Bottom-charmed meson spectrum from a QCD approach based on the Tamm-Dancoff approximation

The bottom-charmed meson spectrum is studied in this work via an effective version of the Coulomb gauge QCD Hamiltonian. The Tamm-Dancoff approximation is employed to estimate the energies of the low-lying and radial-excited $B_c$ states with quantum numbers $J^P = 0^{-}, 0^{+}, 1^{-}, 1^{+}, 2^{+}, 2^{-}$. In particular, we analyze the effects of incorporating an effective transverse hyperfine interaction and spin mixing. The Regge trajectories and hyperfine splitting of both $S$- and $P$-wave states are also examined. The numerical results are compared with available experimental data and theoretical predictions of other models.

Precision laser spectroscopy of the 2S01–3D21 two-photon transition in He3

We have measured the absolute frequency of the $2^{1}S_{0}--3^{1}D_{2}$ two-photon transitions in $^{3}\mathrm{He}$ at 1009 nm based on a cesium frequency standard through an optical frequency comb. The measured frequencies are 594 384 961.072(19) MHz for the $2^{1}S_{0,1/2}--3^{1}D_{2,5/2}$ transition and 594 384 821.209(15) MHz for the $2^{1}S_{0,1/2}--3^{1}D_{2,3/2}$ transition with relative uncertainties of $2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$ and $3.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$, respectively. The determination of the $2^{1}S_{0}--3^{1}D_{2}$ two-photon transition frequency, without hyperfine effect, in $^{3}\mathrm{He}$ is 594 384 761.556(12) MHz. The deduced isotope shift between $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ is 29.530246(18) GHz. The difference of the squares of the nuclear charge radii is deduced to be $1.059(25)\phantom{\rule{4pt}{0ex}}{\mathrm{fm}}^{2}$. Finally, by combining other precise measured transitions, we are able to derive the $3^{3}D_{1}--3^{1}D_{2}$ separation in $^{3}\mathrm{He}$ to be 101 058 203(56) kHz, which is an improvement by a factor of 89 compared to previous work.

Fifth force and hyperfine splitting in bound systems

Two recent experimental observations at the ATOMKI Institute of the Hungarian Academy of Sciences (regarding the angular emission pattern of electron-positron pairs from nuclear transitions from excited states in 8Be and 4He) indicate the possible existence of a particle of a rest mass energy of roughly 17 MeV. The so-called X17 particle constitutes a virtual state in the process, preceding the emission of the electron-positron pair. Based on the symmetry of the nuclear transitions ($1^+$ to $0^+$ and $0^-$ to $0^+$), the X17 could either be a vector, or a pseudoscalar particle. Here, we calculate the effective potentials generated by the X17, for hyperfine interactions in simple atomic systems, for both the pseudoscalar as well as the vector X17 hypotheses. The effective Hamiltonians are obtained in a general form which is applicable to both electronic as well as muonic bound systems. The effect of virtual annihilation and its contribution to the hyperfine splitting also is considered. Because of the short range of the X17-generated potentials, the most promising pathway for the observation of the X17-mediated effects in bound systems concerns hyperfine interactions, which, for $S$ states, are given by modifications of short-range (Dirac-delta) potentials in coordinate space. For the pseudoscalar hypothesis, the exchange of one virtual X17 quantum between the bound lepton and the nucleus exclusively leads to hyperfine effects, but does not affect the Lamb shift. Effects due to the X17 are shown to be drastically enhanced for muonic bound systems. Prospects for the detection of hyperfine effects mediated by X17 exchange are analyzed for muonic deuterium, muonic hydrogen, muonium, true muonium ($\mu^+\mu^-$ bound system), and positronium.

Electron-Electron Dipolar Interaction Poses a Challenge to the Radical Pair Mechanism of Magnetoreception.

A visual magnetic sense in migratory birds has been hypothesized to rely on a radical pair reaction in the protein cryptochrome. In this model, magnetic sensitivity originates from coherent spin dynamics, as the radicals couple to magnetic nuclei via hyperfine interactions. Prior studies have often neglected the electron–electron dipolar (EED) coupling from this hypothesis. We show that EED interactions suppress the anisotropic response to the geomagnetic field by the radical pair mechanism in cryptochrome and that this attenuation is unlikely to be mitigated by mutual cancellation of the EED and electronic exchange coupling, as previously suggested. We then demonstrate that this limitation may be overcome by extending the conventional model to include a third, nonreacting radical. We predict that hyperfine effects could work in concert with three-radical dipolar interactions to tailor a superior magnetic response, thereby providing a new principle for magnetosensitivity with applications for sensing, navigation, and the assessment of biological magnetic field effects.