13C dynamic nuclear polarization in diamond via a microwave-free 'integrated' cross effect

Color-center-hosting semiconductors are emerging as promising source materials for low-field dynamic nuclear polarization (DNP) at or near room temperature, but hyperfine broadening, susceptibility to magnetic field heterogeneity, and nuclear spin relaxation induced by other paramagnetic defects set practical constraints difficult to circumvent. Here, we explore an alternate route to color-center-assisted DNP using nitrogen-vacancy (NV) centers in diamond coupled to substitutional nitrogen impurities, the so-called P1 centers. Working near the level anti-crossing condition - where the P1 Zeeman splitting matches one of the NV spin transitions - we demonstrate efficient microwave-free 13C DNP through the use of consecutive magnetic field sweeps and continuous optical excitation. The amplitude and sign of the polarization can be controlled by adjusting the low-to-high and high-to-low magnetic field sweep rates in each cycle so that one is much faster than the other. By comparing the 13C DNP response for different crystal orientations, we show that the process is robust to magnetic field/NV misalignment, a feature that makes the present technique suitable to diamond powders and settings where the field is heterogeneous. Applications to shallow NVs could capitalize on the greater physical proximity between surface paramagnetic defects and outer nuclei to efficiently polarize target samples in contact with the diamond crystal

Discourse over the sustainability of irrigation with desalinated water in light of the water-energy-food nexus

This is the final version. Available from EWRA via the link in this recordDesalinated seawater has gained increasing popularity as an option for water-stressed regions worldwide to meet a general increase in water demand across most sectors. Considering current water and food crises that are exacerbating in many regions, desalination has gained traction as a suitable solution to alleviate these problems as a potentially limitless alternative water source. The agricultural industry is the largest global water consumer and the sector that is most likely to benefit from this technology to meet the increasing demand for irrigation. Despite the technology’s considerable potential, there are numerous issues related the technology’s sustainability that may prevent it from becoming a widely used solution for irrigation purposes. However, being affected by numerous interconnected factors, water resources problems are nuanced and multi-disciplinary. To account for these intricacies in the evaluation of the sustainability of this option for irrigation, the concept of the Water-Energy-Food (WEF) Security Nexus can be used. This paper provides a preliminary evaluation of the sustainability of the use of desalinated water for irrigation considering the WEF Security Nexus

Spin dynamics of ZnSe-ZnTe nanostructures grown by migration enhanced molecular beam epitaxy

We study the spin dynamics of ZnSe layers with embedded type-II ZnTe quantum dots using time resolved Kerr rotation (TRKR). Three samples were grown with an increasing amount of Te, which correlates with increased quantum dot (QD) density. Samples with a higher quantum dot density exhibit longer electron spin lifetimes, up to 1 ns at low temperatures. Tellurium isoelectronic centers, which form in the ZnSe spacer regions as a result of the growth conditions, were probed via spectrally dependent TRKR. Temperature dependent TRKR results show that samples with high QD density are not affected by an electron-hole exchange dephasing mechanism

Unusual two-dimensional behavior of iron-based superconductors with low anisotropy

© 2017 American Physical Society. We study angular-dependent magnetoresistance in iron-based superconductors Ba1-xNaxFe2As2 and FeTe1-xSex. Both superconductors have relatively small anisotropies γ∼2 and exhibit a three-dimensional (3D) behavior at low temperatures. However, we observe that they start to exhibit a profound two-dimensional behavior at elevated temperatures and in applied magnetic field parallel to the surface. We conclude that the unexpected two-dimensional (2D) behavior of the studied low-anisotropic superconductors is not related to layeredness of the materials, but is caused by appearance of surface superconductivity when magnetic field exceeds the upper critical field Hc2(T) for destruction of bulk superconductivity. We argue that the corresponding 3D-2D bulk-to-surface dimensional transition can be used for accurate determination of the upper critical field

Spin dynamics of a solid-state qubit in proximity to a superconductor

A broad effort is underway to understand and harness the interaction between superconductors and spin-active color centers with an eye on the realization of hybrid quantum devices and novel imaging modalities of superconducting materials. Most work, however, overlooks the complex interplay between either system and the environment created by the color center host. Here we use an all-diamond scanning probe to investigate the spin dynamics of a single nitrogen-vacancy (NV) center proximal to a high-critical-temperature superconducting film in the presence of a weak magnetic field. We find that the presence of the superconductor increases the NV spin coherence lifetime, a phenomenon we tentatively rationalize as a change in the electric noise due to a superconductor-induced redistribution of charge carriers near the NV site. We build on these findings to demonstrate transverse-relaxation-time-weighted imaging of the superconductor film. These results shed light on the complex surface dynamics governing the spin coherence of shallow NVs while simultaneously paving the route to new forms of noise spectroscopy and imaging of superconductors

Multispin-assisted optical pumping of bulk ¹³C nuclear spin polarization in diamond

One of the most remarkable properties of the nitrogen-vacancy (NV) center in diamond is that optical illumination initializes its electronic spin almost completely, a feature that can be exploited to polarize other spin species in their proximity. Here we use field-cycled nuclear magnetic resonance to investigate the mechanisms of spin-polarization transfer from NVs to ¹³C One of the most remarkable properties of the nitrogen-vacancy (NV) center in diamond is that optical illumination initializes its electronic spin almost completely, a feature that can be exploited to polarize other spin species in their proximity. Here we use field-cycled nuclear magnetic resonance to investigate the mechanisms of spin-polarization transfer from NVs to ¹³C spin polarization as a function of the applied magnetic field, we show ¹³C spin pumping takes place via a multispin cross-relaxation process involving the NV⁻ spin and the electronic and nuclear spins of neighboring P1 centers. Further, we find that this mechanism is insensitive to the crystal orientation relative to the magnetic field, although the absolute level of ¹³C polarization—reaching up to ∼3% under optimal conditions—can vary substantially depending on the interplay between optical pumping efficiency, photogenerated carriers, and laser-induced heating

Orientation-independent room temperature optical C-13 hyperpolarization in powdered diamond

Dynamic nuclear polarization via contact with electronic spins has emerged as an attractive route to enhance the sensitivity of nuclear magnetic resonance beyond the traditional limits imposed by magnetic field strength and temperature. Among the various alternative implementations, the use of nitrogen vacancy (NV) centers in diamond—a paramagnetic point defect whose spin can be optically polarized at room temperature—has attracted widespread attention, but applications have been hampered by the need to align the NV axis with the external magnetic field. We overcome this hurdle through the combined use of continuous optical illumination and a microwave sweep over a broad frequency range. As a proof of principle, we demonstrate our approach using powdered diamond with which we attain bulk 13C spin polarization in excess of 0.25% under ambient conditions. Remarkably, our technique acts efficiently on diamond crystals of all orientations and polarizes nuclear spins with a sign that depends exclusively on the direction of the microwave sweep. Our work paves the way toward the use of hyperpolarized diamond particles as imaging contrast agents for biosensing and, ultimately, for the hyperpolarization of nuclear spins in arbitrary liquids brought in contact with their surface