The behavior of a type II superconductor in the presence of a magnetic field is governed by two characteristic length scales, the London penetration depth and the coherence length. We present magnetization measurements on MgB2 powder showing an anisotropy in the upper critical field and hence the coherence length of 6. Using the technique of small angle neutron scattering we show that this anisotropy is not mirrored in the London penetration depth, which is almost isotropic. This result can be explained by the superconductivity residing in two distinct electronic bands of the material, only one of which is highly anisotropic.

Fluorescent nanodiamonds (fNDs) containing nitrogen vacancy (NV) centers are promising candidates for quantum sensing in biological environments. This work describes the fabrication and implementation of electrospun poly lactic‐co‐glycolic acid (PLGA) nanofibers embedded with fNDs for optical quantum sensing in an environment, which recapitulates the nanoscale architecture and topography of the cell niche. A protocol that produces uniformly dispersed fNDs within electrospun nanofibers is demonstrated and the resulting fibers are characterized using fluorescent microscopy and scanning electron microscopy (SEM). Optically detected magnetic resonance (ODMR) and longitudinal spin relaxometry results for fNDs and embedded fNDs are compared. A new approach for fast detection of time varying magnetic fields external to the fND embedded nanofibers is demonstrated. ODMR spectra are successfully acquired from a culture of live differentiated neural stem cells functioning as a connected neural network grown on fND embedded nanofibers. This work advances the current state of the art in quantum sensing by providing a versatile sensing platform that can be tailored to produce physiological‐like cell niches to replicate biologically relevant growth environments and fast measurement protocols for the detection of co‐ordinated endogenous signals from clinically relevant populations of electrically active neuronal circuits.

The nature of the broad band of microscopic excitations measured in molten gallium is investigated by means of analysis of their mode eigenvectors I͑Q , ͒. The results, derived from neutron spectroscopy experiments, show that excitations with a dominant acoustic character are confined to low energy transfers. In contrast, those appearing at higher frequencies unmistakably exhibit optical character, as evidenced by the out-of-phase relationship shown by the phase of oscillations in I͑Q , ͒ that become significantly shifted relative to those of the static structure factor. Such effects are shown to arise from partial covalency that is already known to be present in gaseous, cluster and crystalline forms.

Naturally occurring paramagnetic species (PS), such as free radicals and paramagnetic metalloproteins, play an essential role in a multitude of critical physiological processes including metabolism, cell signaling and immune response. These highly dynamic species can also act as intrinsic biomarkers for a variety of disease states whilst synthetic paramagnetic probes targeted to specific sites on biomolecules enable the study of functional information such as tissue oxygenation and redox status in living systems. The work presented herein describes a new sensing method that exploits the spin dependent emission of photoluminescence (PL) from an ensemble of nitrogen vacancy centers in diamond for rapid, non-destructive detection of PS in living systems. Uniquely this approach involves simple measurement protocols that assess PL contrast with and without the application of microwaves. The method is demonstrated to detect concentrations of paramagnetic salts in solution and the widely used magnetic resonance imaging contrast agent Gadobutrol with a limit of detection of less than 10 attomol over a 100 µm x 100 µm field of view. Real time monitoring of changes in the concentration of paramagnetic salts is demonstrated with image exposure times of 20 ms. Further, dynamic tracking of chemical reactions is demonstrated via the conversion of low spin cyanide coordinated Fe 3+ to hexaaqua Fe 3+ under acidic conditions. Finally, the capability to map paramagnetic species in model cells with sub-cellular resolution is demonstrated using lipid membranes containing gadolinium labelled phospholipids under ambient conditions in the order of minutes. Overall, this work introduces a new sensing approach for the realization of fast, sensitive imaging of PS in a widefield format that is readily deployable in biomedical settings. Ultimately this new approach to NV based quantum sensing paves the way towards minimally invasive real-time mapping and observation of free radicals in in vitro cellular environments.

Detailed high-resolution small-angle neutron diffraction measurements have been used to determine the structural phase diagram of the vortex lattice ͑VL͒ in YNi 2 B 2 C with H ʈ c. At low temperatures ͑T Ӷ T c ͒ the first-order 45°reorientation transition at a field H 1 ͑T͒ and second-order rhombic to square transition, H 2 ͑T͒ have previously been described by the effects of Fermi surface ͑FS͒ anisotropy and nonlocality. H 1 ͑T͒ decreases while H 2 ͑T͒ increases with increasing temperature. Measurements of the VL structure as close to the upper critical field T c2 ͑H͒ as is currently experimentally feasible show no evidence of significant upward curvature or reentrance of H 2 that is expected when thermal fluctuations suppress nonlocality. For fields H 1 ͑T͒ Ͻ H Ͻ H 2 ͑T͒ the VL remains rhombic and shows no sign of becoming hexagonal close to T c2 ͑H͒. Our data suggest that an underlying electronic asymmetry, other than FS and nonlocal effects and likely due to an anisotropic superconducting gap, controls the VL structure close to T c2 ͑H͒.The morphology of the vortex lattice ͑VL͒ in type-II superconductors continues to attract a great deal of interest due to the inherent correlation between the symmetry of the underlying electronic structure, details of the pairing mechanism, and the macroscopic physics of the VL. 1-9 Changes in symmetry and orientation of the VL can arise due to an underlying anisotropy of either the Fermi surface ͑FS͒ or superconducting energy gap. This comes about since the relation between the supercurrent and vector potential of the magnetic induction can be nonlocal, reflecting the finite spatial extent of the cooper pair 0 = v F / ⌬ 0 , where v F is the Fermi velocity and ⌬ 0 is the superconducting gap at zero temperature. For "conventional" type-II superconductors ͑ Ͼ 1/ ͱ 2͒ with an isotropic gap such as Nb, PbTl, and V 3 Si square or rhombic VL structures have been observed for magnetic fields applied along a fourfold symmetry axis. [10][11][12] Kogan et al. 5,6 have been able to describe the structure, orientation, and field dependence of the VL at low temperatures in cubic V 3 Si ͑Ref. 12͒ and the tetragonal rare-earth borocarbides RNi 2 B 2 C ͑Refs. 2 and 3͒ using nonlocal corrections to the London model and estimates for the relevant Fermi velocity averages. In borocarbide superconductors the ͑nearly͒ hexagonal VL undergoes a rhombic distortion with increasing field with the long diagonal along the ͓110͔ direction. This means that the apex angle ␤ is smaller than the usual 60°for a hexagonal VL ͓Fig. 1͑a͔͒. At a field H 1 ͑T͒ the VL undergoes a first-order 45°reorientation and simultaneous jump in ␤ to a value greater than 60°͓Fig. 1͑b͔͒. Increasing field distorts the VL further until a square lattice is formed above H 2 ͑T͒ via a continuous transition. 1-4 In Codoped Lu͑Ni 1−x Co x ͒ 2 B 2 C increasing Co concentration decreases the mean free path l, reducing nonlocal effects, which in turn leads to a rise in H 2 ͑T͒. 13 H 2 ͑T͒ also rises with increasing temperature, again rough...