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

Abstract

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.

Application of spin-exchange relaxation-free magnetometry to the Cosmic Axion Spin Precession Experiment

“…Axions and axion-like particles (ALPs; we do not distinguish between axions and ALPs in the following) have emerged as theoretically well-motivated dark-matter candidates [1,2,3,4,5,6,7]. The Cosmic Axion Spin Precession Experiment (CASPEr) experiment searches for a timevarying axion field by using Nuclear Magnetic Resonance (NMR) techniques [8,9,10,11]. CAPSEr is projected to realize a sensitivity to axions and ALPs beyond the current astrophysical and laboratory limits [9].…”

Invited Review Article: Instrumentation for nuclear magnetic resonance in zero and ultralow magnetic field

“…In low fields, where interactions with the external field are weak compared to spin-spin couplings, there is no truncation and spectra are sharp. [13][14][15] (3) For samples enclosed in metal containers, NMR signals can be strongly attenutated due to the skin-depth effect, which scales with the inverse square root of frequency. At 10 MHz in copper or aluminum the penetration depth is around 20 microns; in contrast, at 1 kHz it is around 2 mm, deep enough to allow signals to pass through the walls of, say, a soda can.…”

Antisymmetric Couplings Enable Direct Observation of Chirality in Nuclear Magnetic Resonance Spectroscopy

“…(1) 0 depends on the handedness of the molecule as shown above. As will be shown in the simulations, the presence of rank-2 couplings (either from the rank-2 J tensor or residual dipolar couplings) give small first-order frequency shifts [28] while J gives a small second-order shift (Fig. 2b) but none of these interfere with chiral discrimination.…”