Quadrupolar Channel Research Articles

Efficient transfer of DNP-enhanced 1 H magnetization to half-integer quadrupolar nuclei in solids at moderate spinning rate.

We show herein how the proton magnetization enhanced by dynamic nuclear polarization (DNP) can be efficiently transferred at moderate magic-angle spinning (MAS) frequencies to half-integer quadrupolar nuclei, S≥3/2, using the Dipolar-mediated Refocused Insensitive Nuclei Enhanced by Polarization Transfer (D-RINEPT) technique, in which a symmetry-based recoupling scheme built from adiabatic inversion 1 H pulses reintroduces the 1 H-S dipolar couplings, while suppressing the 1 H-1 H ones. The use of adiabatic pulses also improves the robustness to offsets and radiofrequency (rf)-field inhomogeneity. Furthermore, the efficiency of the polarization transfer is further improved by using 1 H composite pulses and continuous-wave irradiations between the recoupling blocks, as well as by manipulating the S satellite transitions during the first recoupling block. Furthermore, in the case of large 1 H-S dipolar couplings, the D-RINEPT variant with two pulses on the quadrupolar channel results in an improved transfer efficiency. We compare here the performances of this new adiabatic scheme with those of its parent version with single π pulses, as well as with those of PRESTO and CPMAS transfers. This comparison is performed using simulations as well as DNP-enhanced 27 Al, 95 Mo, and 17 O NMR experiments on isotopically unmodified γ-alumina, hydrated titania-supported MoO3 , Mg(OH)2 , and l-histidine·HCl·H2 O. The introduced RINEPT method outperforms the existing methods, both in terms of efficiency and robustness to rf-field inhomogeneity and offset.

Universal collective modes in two-dimensional chiral superfluids

In this work, we utilize semi-classical kinetic equations to investigate the order parameter collective modes of a class of 2 dimensional superfluids. Extending the known results for $p$-wave superfluids, we show for any chiral ground state of angular momentum $L\geq 1$, there exists a sub-gap mode with mass $\sqrt{2}\, \Delta$ in the BCS limit, where $\Delta$ is the magnitude of the ground state gap. We determine the most significant Landau parameter which contributes to the mass renormalization and show explicitly the renormalized modes become massless at the Pomeranchuk instability of the fermion vacuum. Particularly for $L=1$, we propose a continuous field theory to include the Fermi liquid effect in quadrupolar channel and produce the same result under consistent approximations. They provide potential diagnostics for distinguishing 2 dimensional chiral ground states of different angular momenta with order parameter collective modes and reveal another low energy degrees of freedom near nematic transition.

Detailed analysis of the S-RESPDOR solid-state NMR method for inter-nuclear distance measurement between spin-1/2 and quadrupolar nuclei

We present a detailed analysis of the Symmetry-based Resonance-Echo Saturation-Pulse DOuble-Resonance (S-RESPDOR) method in order to measure the inter-nuclear distances between spin-1/2 and quadrupolar nuclei. This recently introduced sequence employs a symmetry-based recoupling scheme on the observed spin-1/2 channel and a saturation pulse on the quadrupolar channel. This method requires a low radio-frequency (rf) field, is compatible with high MAS frequency and allows a rapid determination of inter-nuclear distances by fitting the experimental signal fraction to an analytical expression. Here, we analyze in detail the influence of the various experimental and spin-interaction parameters on the S-RESPDOR signal fraction and the measured distance. We show that the S-RESPDOR signal fraction only depends on the quadrupole interaction and the inter-nuclear distance. We demonstrate that the required rf-field on the quadrupolar channel is smaller than that required for an adiabatic-passage pulse in REAPDOR-type experiments. The only limitation of the method is the requirement of accurate rotor synchronization between the two parts of the dipolar recoupling sequences. Using S-RESPDOR, we have quantitatively measured a 31P–51V distance of 357pm in a mono-vanadium-substituted polyoxo-tungstate, K4PVW11O40, from the Keggin family and a 13C–67Zn distance of 286pm in [80%–67Zn]zinc [1−13C]acetate. These results show that S-RESPDOR can be employed in the challenging cases of quadrupolar nuclei exhibiting a high spin number and either large chemical-shift anisotropy (51V) or low gyromagnetic ratio (67Zn).

Indirect high-resolution detection for quadrupolar spin-3/2 nuclei in dipolar HMQC solid-state NMR experiments

We present a new kind of NMR pulse sequences to observe heteronuclear correlation (HETCOR) specifically between spin-1/2 and spin-3/2 nuclei with isotropic resolution on the quadrupolar channel. These methods, called HMQC-ST, feature a STMAS filter during the evolution period of the HMQC scheme. Compared to existing HETCOR techniques involving quadrupolar nuclei, the HMQC-ST combines high-resolution and high efficiency and allows indirect detection of spin-3/2 nuclei via sensitive nuclei. We study analytically and using simulations how through-bond and through-space HMQC-ST perform compared to regular HMQC sequence. HMQC-ST potential is demonstrated experimentally by recording through-space HETCOR 2D spectra of Na 2 HPO 4 and NaH 2 PO 4 .

Dilute-bose-gas approach to ground state phases of 3D quantum helimagnets under high magnetic field

We study high-field phase diagram and low-energy excitations of three-dimensional quantum helimagnets. Slightly below the saturation field, the emergence of magnetic order may be mathematically viewed as Bose-Einstein condensation (BEC) of magnons. The method of dilute Bose gas enables an unbiased quantitative analysis of quantum effects in three-dimensional helimagnets and thereby three phases are found: cone, coplanar fan and an attraction-dominant one. To investigate the last phase, we extend the usual BEC approach so that we can handle 2-magnon bound states. In the case of 2-magnon BEC, the transverse magnetization vanishes and long-range order occurs in the quadrupolar channel (spin-nematic phase). As an application, we map out the phase diagram of a 3D helimagnet which consists of frustrated J1-J2 chains coupled by an interchain interaction J3.

Linear beam optics in solenoidal channels

In this paper we study beam transport through a straight solenoidal channel using the single-particle and linear optics approach. We derive the single-particle invariants and show their use in an extended Courant-Snyder theory for a solenoidal coupled system. Matching between solenoidal channels and between solenoidal and quadrupolar channels is discussed. We give envelope solutions and illustrate them with some numerical examples.

X-ray magnetic circular dichroism temperature dependent study of RCo2 compounds

We have performed a temperature-dependent study of the rare earth L2,3 and Co K edges x-ray magnetic circular dichroism (XMCD) in HoCo2 and PrCo2. We have found in both samples that the L2/L3 ratio is temperature independent. This result contradicts previous findings that indicated a possible different behavior for L2 and L3 edges owing to modifications in the degree of 3d–5d hybridization. A further interesting result is that the temperature dependence of ratio E1/E2 for the L3 edge — where E1 and E2 correspond to the two area under the dichroic signal separated in two peaks, positive dipolar dominant, negative with significant contributions of both dipolar and quadrupolar channels — is also constant, suggesting that the dipolar and quadrupolar channels follow the same temperature dependence. This effect might be interpreted as the dominant 4f contribution to the 5d polarization (much larger than the 3d-induced contribution) to create the L-edge XMCD signal. The microscopic origin of the metamagnetic Co subsystem is also addressed.