Nuclear Quadrupole Resonance Experiments Research Articles

Efficient NMR measurement and data analysis supported by the Bayesian inference: The case of the heavy fermion compound YbCo[formula omitted]Zn20

We propose a data-driven technique to infer microscopic physical quantities from nuclear magnetic resonance (NMR) spectra, in which the data size and quality required for the Bayesian inference are investigated. The 59Co-NMR measurement of YbCo2Zn20 single crystal generates complex spectra with 28 peaks. By exploiting the site symmetry in the crystal structure, the isotropic Knight shift Kiso and nuclear quadrupole resonance (NQR) frequency νQ were respectively estimated to be Kiso=0.7822±0.0090% and νQ=2.008±0.016 MHz (T=20 K and H≃10.2 T) by analyzing only 30 data points from one spectrum. The estimated νQ is consistent with the precise value obtained in the NQR experiment. Our method can significantly reduce the measurement time and the computational cost of data analysis in NMR experiments.

Calorimetric measurement of nuclear spin-lattice relaxation rate in metals

The quasiparticle density of states in correlated and quantum-critical metals directly probes the effect of electronic correlations on the Fermi surface. Measurements of the nuclear spin-lattice relaxation rate provide one such experimental probe of quasiparticle mass through the electronic density of states. By far the most common way of accessing the spin-lattice relaxation rate is via nuclear magnetic resonance and nuclear quadrupole resonance experiments, which require resonant excitation of nuclear spin transitions. Here we report non-resonant access to spin-lattice relaxation dynamics in AC-calorimetric measurements. The nuclear spin-lattice relaxation rate is inferred in our measurements from its effect on the frequency dispersion of the thermal response of the calorimeter-sample assembly. We use fast, lithographically-defined nanocalorimeters to access the nuclear spin-lattice relaxation times in metallic indium from 0.3~K to 7~K and in magnetic fields up to 35~T.

A sulfur-33 nuclear quadrupole resonance study of 33 S2 -labeled L-cystine.

The sulfur electric-field-gradient tensor for a disulfide bond in 33 S2 -labeled L-cystine has been investigated by 33 S nuclear quadrupole resonance (NQR). 33 S2 -labeled L-cystine is synthesized by introduction of disulfide ions prepared from elemental 33 S-sulfur into an amino acid derivative, the side chain of which is iodinated. In its NQR spectrum, sharp single peaks are observed at between 24.63 and 24.90 MHz in the temperature range from 80 to 298 K. The two-dimensional nutation echo 33 S NQR experiment is carried out at 160 K, and the quadrupole coupling constant, CQ , and the asymmetric parameter, ηQ , are obtained to be 46.9(9)MHz and 0.6(1), respectively. The calculated 33 S electric-field-gradient tensor components with respect to the molecular frame is briefly discussed.

Novel Approach to the Best-Known Antiferroquadrupolar Material

Nuclear quadrupole resonance (NQR) experiments were performed on CeB6 in an extremely-low-frequency range. These experiments revealed a clear anomaly in the NQR frequency at the antiferroquadrupolar transition of f electrons, albeit with no line splitting or broadening. The results pose a new question regarding the most prominent multipolar materials studied for over 40 years.

Possible New State in CeB6 Uncovered by Extremely Low-Frequency Nuclear Quadrupole Resonance Experiments

Extremely low-frequency nuclear quadrupole resonance analyses of CeB6, a prototypical antiferroquadrupole (AFQ) material, indicate the possible existence of a new state in the zero-field AFQ ordered phase.

Field-Stepwise-Swept Solid-State 35Cl NMR and NQR of trichloroisocyanuric acid

Field-stepwise-swept solid-state 35Cl nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments of trichloroisocyanuric acid (TCICA) are carried out. The quadrupolar frequencies, vQ, were found to be 57.9 – 58.8 MHz in the temperature range between 180 and 299 K. The analysis of the field-stepwise-swept solid-state 35Cl NMR spectrum, observed at 240 K and acquired at 43.25 MHz, yields the quadrupolar coupling constant (CQ) of 116.6(2) MHz and the asymmetric parameter (ηQ) of 0.05(5). The tensor orientation of the 35Cl Electric-Field-Gradient (EFG) tensor is briefly discussed.

Determination of the magnetic q vectors in the heavy fermion superconductor Ce3PtIn11

An analysis with a transferred hyperfine field has been performed on the spectra of the $^{115}\mathrm{In}$ nuclear quadrupole resonance experiments of heavy fermion superconductor ${\mathrm{Ce}}_{3}{\mathrm{PtIn}}_{11}$ exhibiting co-occurrence of two successive antiferromagnetic orderings (${T}_{\mathrm{N}1}$ = 2.2 K and ${T}_{\mathrm{N}2}$ = 2.0 K) followed by a superconducting transition (${T}_{\mathrm{c}}$ = 0.32 K). The spectral changes at magnetic transition temperatures ${T}_{\mathrm{N}1}$ and ${T}_{\mathrm{N}2}$ indicate that the Ce(2) site has the dominant magnetic contribution, with a small magnetic moment, but not negligible, at the Ce(1) site. Our analysis using a transferred hyperfine field which overcomes the previous simple dipolar model evinces the magnetic structures of ${\mathrm{Ce}}_{3}{\mathrm{PtIn}}_{11}$. $\mathrm{For}{T}_{\mathrm{N}2}<T<{T}_{\mathrm{N}1}$, the propagation vectors at the Ce(1) and Ce(2) sublattices are ${\mathbit{q}}_{1}={\mathbit{q}}_{2}=(\frac{1}{2},\phantom{\rule{0.16em}{0ex}}\frac{1}{2},\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}\phantom{\rule{4.pt}{0ex}}\text{or}\phantom{\rule{4.pt}{0ex}}\phantom{\rule{0.16em}{0ex}}\frac{1}{2})$. On the other hand, for $T<{T}_{\mathrm{N}2}$, the propagation vectors are ${\mathbit{q}}_{1}=(\frac{1}{2},\phantom{\rule{0.16em}{0ex}}\frac{1}{2},\phantom{\rule{0.16em}{0ex}}\frac{1}{6}\phantom{\rule{0.16em}{0ex}}\text{or}\phantom{\rule{4.pt}{0ex}}\phantom{\rule{0.16em}{0ex}}\frac{1}{3})$ and ${\mathbit{q}}_{2}=(\frac{1}{2},\phantom{\rule{0.16em}{0ex}}\frac{1}{2},\phantom{\rule{0.16em}{0ex}}\frac{1}{2}\phantom{\rule{0.16em}{0ex}}\phantom{\rule{4.pt}{0ex}}\text{or}\phantom{\rule{4.pt}{0ex}}\phantom{\rule{0.16em}{0ex}}0)$, respectively.

Equatorial Electronic Structure in the Uranyl Ion: Cs2UO2Cl4 and Cs2UO2Br4.

Electric field gradient (EFG) tensors in the equatorial plane of the linear UO22+ ion have been measured by nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments and computed by relativistic Kohn-Sham methods with and without environment embedding for Cs2UO2Cl4 and Cs2UO2Br4. This approach expands the possibilities for probing the electronic structure in uranyl complexes beyond the strongly covalent U-O bonds. The combined analyses find that one of the two largest principal EFG tensor components at the halogen sites points along the U-X bond (X = Cl, Br), and the second is parallel to the UO22+ ion; in Cs2UO2Cl4, the components are nearly equal in magnitude, whereas in Cs2UO2Br4, due to short-range bromide-cesium interactions, the equatorial component is dominant for one pair of Br sites and the axial component is larger for the second pair. The directions and relative magnitudes of the field gradient principal axes are found to be sensitive to the σ and π electron donation by the ligands and the model of the environment. Chlorine-35 NQR spectra of 235U-depleted and 235U-enriched Cs2UO2Cl4 exhibited no uranium-isotope-dependent shift, but the resonance of the depleted sample displayed a 58% broader line width.

Исследование процесса релаксации напряжений в деформированном композите с эпоксидной матрицей

The present paper gives results from a study of the relaxation of internal stresses in a granular composite with an epoxy matrix. We studied samples of ED-20 epoxy resins cured by polyethylene polyamine. As the filler we used powdered copper oxide with a volumetric concentration 0 . 064–0 . 35. The samples had the shape of cylinders of diameter 8 mm and height 30 mm. The experiments are performed with the use of nuclear quadrupole resonance (NQR). Measurements are made of the 63-Cu NQR-frequencies in samples as of epoxy resin containing cuprous oxide powder as control sample – pure cuprous oxide powder. In the description of the results of the NQR experiments, the value of internal stresses is given in frequency units. We held experimental research on cylindrical samples of granular composite with epoxy matrix hardened at high temperature. These samples were subjected to uniaxial compression at room temperature. Deformation of the samples led to an increase NQR frequency of the filler. The change in the value of internal stresses during heating of deformed samples of a granular composite was experimentally investigated. Measurements were made of the frequency difference for copper oxide in the polymer and control samples in the temperature range 393–293 K at 10 K intervals. Stresses in the matrix and the frequency difference decreases with increasing temperature. The observed nonlinearity of the temperature dependences of the NQR frequencies for the filler indicates the presence of relaxation processes in the stressed matrix of the samples at temperatures below the glass transition temperature. It is shown that the process of relaxation of stresses caused by the deformation of the sample is well described by an exponential dependence. The activation energy of this process was 105 kJ / mol. Comparison of the calculation results with the experimental data has shown their satisfactory comparability. Similar experiments were conducted with samples having an epoxy matrix cured at room temperature. It was found that stress relaxation occurs at temperatures well below the glass-transition temperatures.

An automated instrument for polarization-enhanced broadband nuclear quadrupole resonance (NQR) spectroscopy.

An automated instrument for improving the sensitivity of nuclear quadrupole resonance (NQR) spectroscopy is presented. The device is capable of pre-polarizing samples within a custom Halbach-type permanent magnet and then moving them into an external probe for zero-field NQR detection. Polarization transfer between protons and nitrogen (14N) nuclei in the sample occurs during demagnetization, thus increasing the amplitude of the detected NQR signals. The sample motion profile is completely programmable, thus providing a high level of control over the sample position and velocity for optimizing the polarization transfer process for various samples. Moreover, the magnet and motion controller are combined with a shielded sample probe and ultra-broadband front-end electronics (both designed in-house) to realize a complete scientific instrument for 14N NQR experiments. Compared with previous work in the field, the system is designed to be programmable, robust, and easy to use. Experimental results from several samples are also presented.

Model - free approach to quadrupole spin relaxation in solid 209Bi-aryl compounds.

Nuclear Quadrupole Resonance (NQR) experiments were performed for deuterated and non-deuterated triphenylbismuth (BiPh3) to inquire into 209Bi relaxation mechanisms. The studies are motivated by the idea of exploiting Quadrupole Relaxation Enhancement (QRE) as a novel contrast mechanism for Magnetic Resonance Imaging. From this perspective relaxation features of nuclei possessing quadrupole moment (quadrupole nuclei) are of primary importance for the contrast effect. Spin-spin relaxation rates associated with the NQR lines were described in terms of the Redfield relaxation theory assuming that the relaxation is caused by fluctuations of the electric field gradient tensor at the position of the quadrupole nucleus that are described by an exponential correlation function. The description referred to as a model-free approach is an analogy of the description used for paramagnetic contrast agents. It was demonstrated that for the deuterated compound this approach captures the essential features of 209Bi relaxation, but it should not be applied for non-deuterated compounds as dipolar interactions between neighbouring protons and the quadrupole nucleus considerably contribute to the relaxation of the last one. Thus, the relaxation scenario for species containing quadrupole nuclei is fundamentally different than for paramagnetic contrast agents and this fact has to be taken into account when predicting contrast effects based on QRE.

A high-temperature quantum spin liquid with polaron spins

The existence of a quantum spin liquid (QSL) in which quantum fluctuations of spins are sufficiently strong to preclude spin ordering down to zero temperature was originally proposed theoretically more than 40 years ago, but its experimental realisation turned out to be very elusive. Here we report on an almost ideal spin liquid state that appears to be realized by atomic-cluster spins on the triangular lattice of a charge-density wave (CDW) state of 1T-TaS$_2$. In this system, the charge excitations have a well-defined gap of $\sim 0.3$ eV, while nuclear magnetic quadrupole resonance and muon spin relaxation experiments reveal that the spins show gapless quantum spin liquid dynamics and no long range magnetic order down to 70~mK. Canonical $T^{2}$ power-law temperature dependence of the spin relaxation dynamics characteristic of a QSL is observed from 200~K to $T_f= 55$ K. Below this temperature we observe a new gapless state with reduced density of spin excitations and high degree of local disorder signifying new quantum spin order emerging from the QSL.

Experimental realization of non-Abelian non-adiabatic geometric gates

The geometric aspects of quantum mechanics are emphasized most prominently by the concept of geometric phases, which are acquired whenever a quantum system evolves along a path in Hilbert space, that is, the space of quantum states of the system. The geometric phase is determined only by the shape of this path and is, in its simplest form, a real number. However, if the system has degenerate energy levels, then matrix-valued geometric state transformations, known as non-Abelian holonomies--the effect of which depends on the order of two consecutive paths--can be obtained. They are important, for example, for the creation of synthetic gauge fields in cold atomic gases or the description of non-Abelian anyon statistics. Moreover, there are proposals to exploit non-Abelian holonomic gates for the purposes of noise-resilient quantum computation. In contrast to Abelian geometric operations, non-Abelian ones have been observed only in nuclear quadrupole resonance experiments with a large number of spins, and without full characterization of the geometric process and its non-commutative nature. Here we realize non-Abelian non-adiabatic holonomic quantum operations on a single, superconducting, artificial three-level atom by applying a well-controlled, two-tone microwave drive. Using quantum process tomography, we determine fidelities of the resulting non-commuting gates that exceed 95 per cent. We show that two different quantum gates, originating from two distinct paths in Hilbert space, yield non-equivalent transformations when applied in different orders. This provides evidence for the non-Abelian character of the implemented holonomic quantum operations. In combination with a non-trivial two-quantum-bit gate, our method suggests a way to universal holonomic quantum computing.

Dimensionality of Spin Modulations in 1/8-Doped Lanthanum Cuprates from the Perspective of NQR and μSR Experiments

We investigate the dimensionality of inhomogeneous spin modulation patterns in the cuprate family of high-temperature superconductors with particular focus on 1/8-doped lanthanum cuprates. We compare one-dimensional stripe modulation pattern with two-dimensional checkerboard of spin vortices in the context of nuclear quadrupole resonance (NQR) and muon spin rotation (μSR) experiments. In addition, we also consider the third pattern, a two-dimensional superposition of spin spirals. Overall, we have found that none of the above patterns leads to a consistent interpretation of the two types of experiments considered. This, in particular, implies that the spin vortex checkerboard cannot be ruled out on the basis of available NQR/μSR experimental results.

Local electric state of noncentrosymmetric superconductor Mo3Al2C revealed by Mo NQR and NMR experiments

Mo nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements were performed on a noncentrosymmetric superconductor Mo3Al2C to investigate the local electronic state at Mo nuclei, which carries the electrons responsible for superconductivity. The NQR frequency, which is linked to the electric field gradient at Mo site, was determined from 95Mo NMR spectrum and the result was verified by the independent 97Mo NQR measurement. The experimentally obtained value is compared to the result of a point charge calculation to extract the EFG induced by conduction electrons and reveal the local electronic state.

Quantum information processing by nuclear magnetic resonance on quadrupolar nuclei

Nuclear magnetic resonance is viewed as an important technique for the implementation of many quantum information algorithms and protocols. Although the most straightforward approach is to use the two-level system composed of spin 1/2 nuclei as qubits, quadrupolar nuclei, which possess a spin greater than 1/2, are being used as an alternative. In this study, we show some unique features of quadrupolar systems for quantum information processing, with an emphasis on the ability to execute efficient quantum state tomography (QST) using only global rotations of the spin system, whose performance is shown in detail. By preparing suitable states and implementing logical operations by numerically optimized pulses together with the QST method, we follow the stepwise execution of Grover's algorithm. We also review some work in the literature concerning the relaxation of pseudo-pure states in spin 3/2 systems as well as its modelling in both the Redfield and Kraus formalisms. These data are used to discuss differences in the behaviour of the quantum correlations observed for two-qubit systems implemented by spin 1/2 and quadrupolar spin 3/2 systems, also presented in the literature. The possibilities and advantages of using nuclear quadrupole resonance experiments for quantum information processing are also discussed.

75As NMR-NQR study in superconducting LiFeAs

We report results of 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments as well as 7Li NMR on different samples of self flux grown LiFeAs and 5 % Co doped LiFeAs single crystals, and a polycrystalline LiFeAs sample. We were able to distinguish the samples by their slightly different quadrupole frequencies, $\nu_Q$, which is a direct measure of the electric field gradient (EFG) at the As site. Interestingly, samples with a large quadrupole frequency appear to show a different Knight shift and spin lattice relaxation in the superconducting state from those with a lower $\nu_Q$, yet all the samples are clearly superconducting. For sample S1 which has the largest $\nu_Q$, we find constant Knight shift K across Tc for a certain direction of the magnetic field and a peculiar upturn of the NQR spin lattice relaxation rate 1/T1 below Tc. In contrast, samples with a lower $\nu_Q$ exhibit the expected behavior for a singlet superconductor: a drop of K and 1/T1 for both NMR and NQR below Tc. Our results show that already tiny changes in stoichiometry uncovered by slightly different NQR frequencies lead to very different behavior of the NMR parameters in the superconducting state of LiFeAs. Different possibilities will be discussed which may explain the contrasting behavior.

Direct Investigation of Covalently Bound Chlorine in Organic Compounds by Solid‐State 35Cl NMR Spectroscopy and Exact Spectral Line‐Shape Simulations

35/37Cl NMR spectroscopy studies of organic systems are very rare, with only a few neat liquids having been studied.1 The lack of chlorine NMR spectroscopy data may be explained by the fact that 35Cl and 37Cl are quadrupolar (spin I=3/2) and low-frequency isotopes. The quadrupole moments of the chlorine nuclei couple with the electric field gradient (EFG) tensor at the nuclei; this phenomenon is known as the quadrupolar interaction (QI). The quadrupolar coupling constant, CQ, and the quadrupolar asymmetry parameter, ηQ, describe the magnitude and asymmetry of the QI. In solution, one of the consequences of the QI is fast relaxation, which means that the 35/37Cl NMR signals for covalently bound chlorines are very broad and are of low intensity.1 For these reasons, chemically distinct chlorine sites are very difficult to distinguish with solution NMR spectroscopy. However, in the solid state, nuclear spin relaxation is typically slower, thus enabling higher quality 35Cl NMR spectra to be collected, at least in principle. Unfortunately, the magnitude of the QI for covalently bound chlorines is very large because of the substantial, anisotropic EFG at the Cl atom, owing mainly to its electronic configuration when it forms a chlorine–carbon bond. Conventional wisdom is that such chlorine sites cannot be studied in powders by solid-state NMR spectroscopy as the central transition (CT; mI=1/2↔−1/2) can span tens of megahertz in typical commercially available magnetic fields. For this reason, only ionic chlorides2 and inorganic chlorides3 have been studied, as the EFG at these chlorides is often an order of magnitude smaller than at covalently bound chlorine atoms in organic molecules. The bonding environments for these types of chlorine atoms are substantially different from the environments in those chloride-containing molecules that have been studied previously.2, 3 A partial 35Cl NMR spectrum for hexachlorophene has been briefly mentioned in the literature.4 On the other hand, most of the interesting chlorine chemistry occurs when Cl is covalently bound to a carbon atom, where the chlorine atom often acts as a leaving group. Chlorine atoms are also important in many organic pharmaceuticals as well as in crystal design applications where they can form halogen bonds.5 Recent studies show that covalently bound chlorine is also important in biological chemistry where, for example, the tryptophan 7-halogenase was found to selectively chlorinate tryptophan moieties.6

Using 69/71Ga solid-state NMR and 127I NQR as probes to elucidate the composition of “GaI”

While the synthetic utility and reactivity of the so-called “GaI” species is reasonably well established, its exact composition remains unknown. Using primarily multinuclear magnetic resonance techniques (and supported with powder X-ray diffraction measurements), we offer some new insights into the composition of “GaI”. Using 127I nuclear quadrupole resonance (NQR) experiments, it is clearly demonstrated that gallium diiodide (GaI2) is a significant component of this material, while GaI3 is not. This finding is in contrast with a prior literature account, which noted that Ga2I3 (i.e., one equivalent of GaI3 per equivalent of Ga metal) was present in significant amounts. Additional solid-state nuclear magnetic resonance (SSNMR) experiments using the 69/71Ga probe nuclei in multiple magnetic fields clearly establish, via its diagnostic Knight-shifted resonance, the presence of Ga0 metal, which is in agreement with prior literature. Taken together, a composition may be tentatively offered: that “GaI” is, to a large extent, two equivalents of Ga0 metal with two equivalents of GaI2, where the latter is composed of Ga+ and GaI4- ions. This composition may be represented as [Ga0]2[Ga]+[GaI4]−.

PEANUT experiment in NQR spectroscopy for I=3/2

The experiment with phase inversion and phase-inverted echo-amplitude detected nutation (PEANUT) was introduced in the nuclear quadrupole resonance (NQR). Formulas were obtained describing the NQR (I=3/2) experiment. Exemplary experiments are provided confirming the predicted particularities of the PEANUT spectra in NQR Cl-35. It is proposed to apply the method for the purpose of determination the asymmetry parameter of the electric field gradient (EFG) tensor in powders with the help of the analysis of PEANUT interferograms. Application of two-dimensional PEANUT experiments, in which the nutation frequencies correlate with the resonance NQR frequencies, can substantially simplify the interpretation of complex spectra.