Quadrupole Resonance Research Articles

Ab initio electronic factors of the A and B hyperfine structure constants for the 5s25p6sP1o1,3 states in Sn i

Large-scale $\textit{ab initio}$ calculations of the electric field gradient, which constitutes the electronic contribution to the electric quadrupole hyperfine constant $B$, were performed for the $5s^25p6s$ $^{1,3}\!P^{\rm o}_1$ excited states of tin, using three independent computational strategies of the variational multiconfiguration Dirac-Hartree-Fock method and a fourth approach based on the configuration interaction Dirac-Fock-Sturm theory. For the $5s^25p6s$ $^{1}\!P^{\rm o}_1$ state, the final value of $B/Q =703(50)$ MHz/b differs by $0.4\%$ from the one recently used by Yordanov ${\it et~al.}$ [Communications Physics ${\bf 3}$, 107 (2020)] to extract the nuclear quadrupole moments, $Q$, for tin isotopes in the range $^{(117-131)}$Sn from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final $B/Q$ value of the $5s^25p6s\,^{1}\!P^{\rm o}_1$ state based on statistical principles and on correlation with the magnetic dipole hyperfine constant $A$.

Manipulation of quantum dot emission with semiconductor metasurfaces exhibiting magnetic quadrupole resonances.

Optical metasurfaces were suggested as a route for engineering advanced light sources with tailored emission properties. In particular, they provide a control over the emission directionality, which is essential for single-photon sources and LED applications. Here, we experimentally study light emission from a metasurface composed of III-V semiconductor Mie-resonant nanocylinders with integrated quantum dots (QDs). Specifically, we focus on the manipulation of the directionality of spontaneous emission from the QDs due to excitation of different magnetic quadrupole resonances in the nanocylinders. To this end, we perform both back focal plane imaging and momentum-resolved spectroscopy measurements of the emission. This allows for a comprehensive analysis of the effect of the different resonant nanocylinder modes on the emission characteristics of the metasurface. Our results show that the emission directionality can be manipulated by an interplay of the excited quadrupolar nanocylinder modes with the metasurface lattice modes and provide important insights for the design of novel smart light sources and new display concepts.

Continuous random network avoidance and microscopic relaxation time in As2Se3 glass

Recent nuclear magnetic resonance (NMR) studies on SiO2 structural glass has shown a positive correlation exists between Si-O bond lengths and Si-O-Si bond angles. This indicates that when the glass solidified it avoided forming as a continuous random network (CRN). A microscopic tight binding (TB) model was used some years ago to predict the nuclear quadrupole resonance (NQR) distribution of powdered As2Se3 glass. Similar bond length- bond angle correlations were found. Here we extend this model and show that these correlations are directly attributable to a competition between valence electronic energy and emergent frustration forces as the glass solidifies into a locally preferred structure (LPS). Recent studies have shown that fast atomic motion occurs in metallic glasses at temperatures far below the glass temperature. Using this model we calculate a microscopic relaxation time and show it is a product of CRN avoidance.

Validation of an optical potential for incident and emitted low-energy alpha -particles in the Asim 60 mass range

A consistent set of statistical-model input parameters, validated by analysis of various independent data, makes possible the assessment of an alpha -particle optical model potential [Phys. Rev. C 90, 044612 (2014)] also for nucleon-induced alpha -emission within the A sim 60 mass-number range. The advantage of recent data for low-lying states feeding is taken as well. Consideration of additional reaction channels leading to increase of the alpha -emission beyond the statistical predictions has concerned the pickup direct interaction and Giant Quadrupole Resonance similar features.

Microscopic evidence for the intra-unit-cell electronic nematicity inside the pseudogap phase in YBa2Cu4O8

Understanding the nature of the mysterious pseudogap phenomenon is one of the most important issues associated with cuprate high-Tc superconductors. Here, we report 17O nuclear magnetic resonance (NMR) studies on two planar oxygen sites in stoichiometric cuprate YBa2Cu4O8 to investigate the symmetry breaking inside the pseudogap phase. We observe that the Knight shifts of the two oxygen sites are identical at high temperatures but different below Tnem ∼ 185 K, which is close to the pseudogap temperature T*. Our result provides a microscopic evidence for intra-unit-cell electronic nematicity. The difference in quadrupole resonance frequency between the two oxygen sites is unchanged below Tnem, which suggests that the observed nematicity does not directly stem from the local charge density modulation. Furthermore, a short-range charge density wave (CDW) order is observed below T ≃ 150 K. The additional broadening in the 17O-NMR spectra because of this CDW order is determined to be inequivalent for the two oxygen sites, which is similar to that observed in case of nematicity. These results suggest a possible connection between nematicity, CDW order, and pseudogap.

A Terahertz gradient metasurface based on hybridized dipole and quadrupole resonances

Metasurfaces have demonstrated a wide range of functions, including guided scattering and localization of electromagnetic waves, and they are a promising platform for replacing bulk components in the Terahertz frequency range. Nevertheless, precise local control of the scattered wave on a very subwavelength scale remains a challenge, with high magnitude and full 2π phase tuning being difficult to achieve with a single resonance structure. Here, we present a simple deeply subwavelength (λ/16) metamaterial unit cell based upon the coupling of dipole and quadrupole resonances, which achieves complete phase coverage as well as high reflection magnitude. We numerically demonstrate high efficiency anomalous reflection (81%) at an angle of 45°, avoiding almost all other spurious diffraction orders (0.15%). We also design a structure with a lower reflection angle of 25°, where efficiency is expected to degrade due to the presence of higher order Floquet modes. However, we observe that efficiency remains high (∼ 85%) with 0.58% spurious reflections. Hence, our design can be used in a variety of applications such as beam forming and scanning antennas, reflectarray antennas, phase shifters and beam splitters.

Graphene-tuned threshold gain to achieve optical pulling force on microparticle* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11904184, 11847033, and 11704158) and the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20170170).

We investigate optical force on a graphene-coated gain microparticle by adopting the Maxwell’s stress tensor method. It is found that there exists a threshold gain in obtaining the Fano-profile optical force which indicates the reversal of optical pushing and pulling force. And giant pushing/pulling force can be achieved if the gain value of the material is in the proximity of the threshold gain. Our results show that the threshold gain is more sensitive to the relaxation time than to the Fermi energy of the graphene. We further study the optical force on larger microparticle to demonstrate the pulling force occurring at octupole resonance with small gain value and then it will appear at quadrupole resonance by increasing gain value. Our work provides an in-depth insight into the interaction between light and gain material and gives the additional degree of freedom to optical manipulation of microparticle.

Steady-State Free Precession and Solid-State NMR: How, When, and Why

Nuclear magnetic resonance (NMR) is a well-established technique, to study crystalline and amorphous solids, that provides rich structural and dynamical insights. Many solids NMR experiments, however, are challenged by sensitivity considerations, which demand the use of optimized data acquisition protocols. When inhomogeneous broadenings dominate the lineshapes, as is often the case when dealing with quadrupolar nuclei, the application of multiple echoes by means of Carr-Purcell Meiboom-Gill (CPMG) sequence variants can considerably facilitate the acquisition of solid-state NMR data. This study explores the use of steady-state free precession (SSFP) experiments, another proposal derived from Carr’s early work. SSFP sequences are commonly utilized in magnetic resonance imaging acquisitions, which are also dominated by (gradient-imposed) inhomogeneous broadenings, where they are well-known to provide the highest sensitivity per unit time. SSFP sequences are also common in nuclear quadrupole resonance—yet to our knowledge they have been less explored within the realm of high-field solids NMR on static and spinning samples. The present study examines the application of SSFP to these scenarios, in particular, in what concerns its ability to enhance the sensitivity of wide-line spectra. The regimes when SSFP could be advantageous compared to CPMG acquisitions are examined, and sensitivity enhancements of between 1 and 2 orders of magnitude per unit time are theoretically predicted and experimentally demonstrated in certain instances. Aspects in need of improvement to enable a wider use of SSFP-based approaches, particularly to wide-line quadrupolar studies, are also examined.

The Use of Marginal Oscillator Detector with Increased Conversion Linearity for Recording Broadband Multiplet Nuclear Quadrupole Resonance Spectra

The Use of Marginal Oscillator Detector with Increased Conversion Linearity for Recording Broadband Multiplet Nuclear Quadrupole Resonance Spectra

High-precision nuclear-quadrupole-resonance thermometer for aerohydrodynamic research

In hydroaerodynamics, there are problems that require increased accuracy of temperature measurement. An example is the measurement of excess temperature at the periphery of turbulent jets. Unlimited temperature increase on the axis of the jet to increase the accuracy of measurement is impractical due to non-automodeliness by the Archimedes number. To do this, it is possible to use the phenomenon of nuclear quadrupole resonance. The device for exact measurement of temperature in the range from 0° C to +200 °C is offered. Using the LabView graphic programming package, a virtual model of an automatic thermometer based on nuclear quadrupole resonance in КClO3 was built. The temperature sensor is a superregenerative spectrometer with automatic monitoring of the center of the absorption line of the thermometric substance, consisting of the actual superregenerator, bandpass filter, comparator, DC amplifier and modulating voltage generator. The circuit that switches the supergenerator to the mode of continuous generation and output of information on the display contains a single vibrator, a buffer stage, a microcontroller and an indicator. From the output of the superregenerator, the absorption signal is fed to the bandpass filter, and then to the comparator. After the comparator, a voltage equal to the input voltage difference is amplified by a DC amplifier. This signal controls the resonant absorption frequency through the feedback circuit. The frequency of the sensor polling is determined by a single vibrator, the oscillations of which are synchronized with the clock generator. Measuring uncertainty in the range above changes from 0.02 K to 0.002 K It has been shown that either a manual frequency measurement method or a regenerative mode must be used to reduce the measurement uncertainty up to 0.002 K in the range. This improved automatic device is more complex, because of requirements of special measures to eliminate parasitic amplitude modulation. To increase the temperature range and precision, it is possible to find other thermometric substance, such as Сu2O crystals.

New findings from old data: A semi-experimental value for the eQq of the nitrogen atom.

Nuclear quadrupole coupling arises from the interaction of the nuclear quadrupole moment with the electric field gradient. Thus, it is associated with electron occupancy and the electronic structure of molecules. We demonstrate a simple method for planar molecules based on a direct correlation between the out-of-plane quadrupole coupling constant and the electron occupancy in the p orbital perpendicular to the molecular plane. This method is applied to 98 molecular systems containing a 14N quadrupolar nucleus using data from more than 40 years of rotational spectroscopy and comparing the performance of three levels of theory from quantum-chemical computations. From this extensive dataset, we have analyzed chemical properties of molecules, such as the hybridization of the atom, and we could quantify the extent of polarization and resonance processes as well as physical characteristics of the quadrupolar nucleus, such as eQq. This is a constant, which represents the interaction in the hypothetical case of having a single electron in an electronic orbital at the isolated nucleus, and its value has been under debate for a long time. Here, the eQq value has been determined for the 14N nucleus, and the methodology to calculate it for other nuclei is provided.

Electronic correlations and crystal-field effects in RCu3Ru4O12 (R=La, Pr, Nd)

Among the large class of $A$-site ordered perovskites of stoichiometry $A{C}_{3}{B}_{4}{\mathrm{O}}_{12}$, the rare-earth $(R)$ ruthenates $R{\mathrm{Cu}}_{3}{\mathrm{Ru}}_{4}{\mathrm{O}}_{12}$ $(R=\mathrm{La}, \mathrm{Pr}, \mathrm{Nd})$ are interesting compounds due both to $\mathrm{Ru}\text{\ensuremath{-}}4d$-derived electronic correlations and to unconventional crystal-electric-field effects of the $R$ ions. Here we report on detailed investigations of these compounds utilizing x-ray diffraction, neutron scattering, magnetic susceptibility, and electrical resistivity measurements as well as heat capacity and nuclear resonance experiments. A broad range of external parameters is scanned and depending on the specific technique, temperatures range from 100 mK to 730 K in external magnetic fields up to 14 T. In this work ${\mathrm{LaCu}}_{3}{\mathrm{Ru}}_{4}{\mathrm{O}}_{12}$ serves as reference compound with a nonmagnetic $A$ site, characterized in detail recently [S. Riegg et al., Phys. Rev. B 93, 115149 (2016)]. All compounds investigated reveal heavy-fermion behavior with a ${T}^{2}$ dependence of the low-temperature electrical resistivity and significantly enhanced Sommerfeld coefficients. Toward low temperatures, the compounds with $R=\mathrm{Pr}$ and Nd are dominated by the magnetic moments of the $R$ ions, which occupy crystallographic positions with point-group symmetry ${T}_{h}$. The crystal-electric-field effects are clearly visible especially in heat capacity and inelastic neutron scattering data from which the crystal-electric-field parameters are derived. The ground state of the ${\mathrm{Pr}}^{3+}$ ion is identified as a triplet $({\mathrm{\ensuremath{\Gamma}}}_{4}^{(1)})$, whereas for ${\mathrm{Nd}}^{3+}$ it is a quartet $({\mathrm{\ensuremath{\Gamma}}}_{67})$. Evidence for lowering of the ${T}_{h}$ symmetry is observed at the Pr site at temperatures below 10 K, suggesting the formation of orbital order. Moreover, the spin-lattice relaxation derived from $^{63}\mathrm{Cu}$ nuclear quadrupole resonance indicates characteristic temperatures close to 7 K and 350 mK, probably related to orbital and magnetic order, respectively.

Investigation of magnetic noise from conductive shields in the 10–300 kHz frequency range

We present experimental and theoretical investigations of magnetic noise originating from radio-frequency (RF) conductive shields of flat geometry in the inductance-dominated impedance regime below 300 kHz. The measurement is based on a Q-factor determination of a coil that provides a sufficient sensitivity, placed at the position where the shield magnetic noise is measured. The theory is based on calculations of magnetic field and inductance of one or a few flat rings that emulate a conductive shield. The theoretical model is found to be in close agreement with experimental data. It can be used to predict the magnetic noise of a conductive shield with different thicknesses, conductivities, and temperatures at different distances for a wide range of frequencies. Although the model can be generalized for a more arbitrary shield geometry, in its presented form, it can be applied to the magnetic noise predictions when the shield surface curvature is not large. One important conclusion is that the RF conductive shield can generate the magnetic noise much lower than femtotesla, and, thus, it can be used in many precision experiments targeting minute high-frequency magnetic signals, such as detection of magnetic resonance imaging and nuclear quadrupole resonance signals and search for axion dark matter.

Ta181 nuclear quadrupole resonance study of the noncentrosymmetric superconductor PbTaSe2

We report on a pure $^{181}$Ta-nuclear quadrupole resonance (NQR) measurement of PbTaSe$_2$ at zero magnetic field, which has the advantage of directly probing the intrinsic superconducting phase and electronic states of the TaSe$_2$ layer. We observed the $^{181}$Ta-NQR spectrum of the intrinsic structure with space group $P6$-$m2$, which agrees well with density functional theory (DFT) calculations. The nuclear spin relaxation rate ($1/T_1$) shows an exponential decrease well below $T_{\rm_c}$, indicating that the superconducting state is fully gapped in the framework of Bardeen-Cooper-Schrieffer (BCS) theory. The gap size obtained by $^{181}$Ta-NQR was smaller than the value in previous reports, which may imply that the Fermi surfaces composed of Ta-5$d$ orbitals, where the average pairing interactions are expected to be weaker than in BCS model, are primarily probed. The temperature dependence of $1/T_1$ below $T_{\rm_c}$ can be reproduced well by the superposition of quadrupole and magnetic relaxation mechanisms, together with the distribution of superconducting gap size inherent to multiple Fermi surfaces theoretically proposed in PbTaSe$_2$.

Microscopic study of shape evolution and ground-state properties of Iodine isotopes

In this paper, we investigated the shape evolution and ground-state properties of 108−144I isotopes using Hartree–Fock-Bogoliubov Model while employing the axially deformed single-particle harmonic oscillator basis for the expansion of quasiparticle wave functions. We have used SKP and UNEDF2 models to perform the theoretical calculations. We have presented the shape evolution and final values of the quadrupole deformation parameter β 2 of iodine isotopes. We have used the final values of the β 2 for studying the ground-state properties of the iodine isotopic chain. The investigated ground-state properties are the nuclear electric quadrupole moment, single-particle energy levels, the binding energy per nucleon, pairing energy, one-neutron separation energy, two-neutron separation energy, nuclear charge radius, neutron rms radius, proton rms radius, and neutron skin thickness. After using the SKP parameterization on 109I, we have observed the shape coexistence of prolate and oblate shape. Similarly, after using the UNEDF2 parameterization on 110I, 112I, 114I, 115I, 116I, 117I, 118I, and 119I, we discover the shape coexistence of prolate and oblate shape.

Search for CP-violating nuclear magnetic quadrupole moment using the LuOH+ cation

The time-reversal and spatial parity violating interaction of the nuclear magnetic quadrupole moment (MQM) of the 175Lu and 176Lu nuclei with electrons in the molecular cation LuOH+ is studied. The resulting effect is expressed in terms of fundamental parameters, such as quantum chromodynamics angle θ¯, quark electric dipole moment (EDM), and chromo-EDM. For this, we have estimated the magnetic quadrupole moments of 175Lu and 176Lu nuclei and calculated the molecular constant that characterizes the interaction of the MQM with electrons in the considered molecules. Additionally, we predict the hyperfine structure constants for the ground electronic state of LuOH+. In the molecular calculations, both the correlation and relativistic effects including the Gaunt interaction have been considered. According to the calculated expressions in terms of the fundamental constants, we conclude that LuOH+ can be a promising system to measure the nuclear MQM.

A Low-Cost Digital Pulsed Coherent Spectrometer for Investigation of NQR in Layered Semiconductor GaSe and InSe Crystals

A low-cost digital pulsed nuclear quadrupole resonance (NQR) radio-spectrometer is proposed, all main modules of digital processing and synthesis of which on the field-programmable gate array (FPGA) are implemented. The input sensitivity of the device is of the order of 3 μV to 5 μV which allows conducting NQR studies in samples of relatively small dimensions. The application of the developed methods of NQR pulsed radio spectroscopy made it possible to increase spectral resolution, improve spectral shape and significantly reduce the time of research. In the case of studying InSe and GaSe crystals, spectra with signal-to-noise ratio (SNR) values of 41.9 dB were observed in samples with a volume of 0.1 cm3. As the results of the research have shown, the characteristics of the proposed spectrometer make it effective when used to observe free induction decay (FID) signals of a significant number of isotopes of elements with quadrupolar nuclei.

57Fe Mössbauer parameters from domain based local pair-natural orbital coupled-cluster theory.

We report on applications of the domain based local pair-natural orbital (PNO) coupled-cluster method within the singles and doubles approximation (DLPNO-CCSD) to the calculation of 57Fe isomer shifts and quadrupole splittings in a small training set of iron complexes consisting of large molecular ligands and iron atoms in varying charge, spin, and oxidation states. The electron densities and electric field gradients needed for these calculations were obtained within the recently implemented analytic derivative scheme. A method for the direct treatment of scalar relativistic effects in the calculation of effective electron densities is described by using the first-order Douglas-Kroll-Hess Hamiltonian and a Gaussian charge distribution model for the nucleus. The performance of DLPNO-CCSD is compared with four modern-day density functionals, namely, RPBE, TPSS, B3LYP, and B2PLYP, as well as with the second-order Møller-Plesset perturbation theory. An excellent correlation between the calculated electron densities and the experimental isomer shifts is attained with the DLPNO-CCSD method. The correlation constant a obtained from the slope of the linear correlation plot is found to be ≈-0.31 a.u.3 mm s-1, which agrees very well with the experimental calibration constant α = -0.31 ± 0.04 a.u.3 mm s-1. This value of a is obtained consistently using both nonrelativistic and scalar relativistic DLPNO-CCSD electron densities. While the B3LYP and B2PLYP functionals achieve equally good correlation between theory and experiment, the correlation constant a is found to deviate from the experimental value. Similar trends are observed also for quadrupole splittings. The value of the nuclear quadrupole moment for 57Fe is estimated to be 0.15 b at the DLPNO-CCSD level. This is consistent with previous results and is here supported by a higher level of theory. The DLPNO-CCSD results are found to be insensitive to the intrinsic approximations in the method, in particular the PNO occupation number truncation error, while the results obtained with density functional theory (DFT) are found to depend on the choice of the functional. In a statistical sense, i.e., on the basis of the linear regression analysis, however, the accuracies of the DFT and DLPNO-CCSD results can be considered comparable.

Development of a Low-Cost, Portable NQR Spectrometer for RDX Explosives Detection

Nuclear quadrupole resonance (NQR) technology is a promising approach to detect so-called “minimum metal” landmines, as it can look directly for their explosive content. Conventional commercially available NQR devices, however, are large and expensive, and they require a transmitter power amplifier with a power generator, which is not suitable for outdoor use and mass production. Here we present a small and inexpensive portable device developed for detecting landmines using NQR. The device uses a field-programmable gate array (FPGA) and low-impedance transmission and reception circuits that include a dual supply class-D power amplifier powered by conventional batteries to ensure sufficient magnetic field excitation for mine detection. The pulse width modulation signals that are fed into the power amplifier have been designed to protect the low impedance transmit-receive switch circuit from the high voltage. The system has been tested successfully in the laboratory with 100g of explosive RDX at a distance of 10cm from the antenna, corresponding to a plausible anti-personal (AP) mine scenario. Detection was achieved with a signal to noise ratio (SNR) ~2 in 2/3 of the time that a previous prototype required (120 sec). Moreover, the new device can detect RDX explosives with a measurement time and SNR comparable to mine detectors built with commercial-off-the-shelf (COTS) components, but at lower cost and smaller form factor.

Isoscalar monopole and quadrupole modes in Mo isotopes: Microscopic analysis

The recent RCNP (α,α′) data on the Isoscalar Giant Monopole Resonance (ISGMR) and Isoscalar Giant Quadrupole Resonance (ISGQR) in 92,94,96,98,100Mo are analyzed within a fully self-consistent Quasiparticle Random Phase Approximation (QRPA) approach with Skyrme interactions, in which pairing correlations and possible axial deformations are taken into account. The Skyrme sets SkM*, SLy6, SVbas and SkPδ, that explore a diversity of nuclear matter properties, are used. We discuss the connection between the line shape of the monopole strength ISGMR and the deformation-induced coupling between the ISGMR and the K=0 branch of the ISGQR. The ISGMR is best described by the force SkPδ, having a low incompressibility K∞=202MeV. The ISGQR data are better reproduced by SVbas, that has large isoscalar effective mass m⁎/m=0.9. The need of a functional that can describe simultaneously the ISGMR and ISGQR data is stressed, with the requirement of suitable values of K∞ and m⁎/m. Possible extensions of the QRPA to deal with soft systems are also envisaged.