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Using small-angle neutron scattering, we have studied the flux-line lattice (FLL) in the superclean, high-kappa superconductor CeCoIn5. The FLL undergoes a first-order symmetry and reorientation transition at approximately 0.55 T at 50 mK. In addition, the FLL form factor in this material is found to be independent of the applied magnetic field, in striking contrast to the exponential decrease usually observed in superconductors. This result is consistent with a strongly field-dependent coherence length, proportional to the vortex separation.

X-ray diffraction studies of fine polycrystalline samples of MgB$_2$ in the superconducting state reveal that crystals orient with their \emph{c}-axis in a plane normal to the direction of the applied magnetic field. The MgB$_2$ samples were thoroughly ground to obtain average grain size 5 - 10 $\mu$m in order to increase the population of free single crystal grains in the powder. By monitoring Bragg reflections in a plane normal to an applied magnetic field we find that the powder is textured with significantly stronger (\emph{0,0,l}) reflections in comparison to (\emph{h,k,0}), which remain essentially unchanged. The orientation of the crystals with the \emph{ab}-plane parallel to the magnetic field at all temperatures below $T_c$ demonstrates that the sign of the torque under magnetic field does not alter, in disagreement with current theoretical predictions.

Using small-angle neutron scattering, we have measured the misalignment between an applied field of $4\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ and the flux-line lattice in $\mathrm{Mg}{\mathrm{B}}_{2}$, as the field is rotated away from the $c$ axis by an angle $\ensuremath{\theta}$. The measurements, performed at $4.9\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, showed the vortices canting towards the $c$ axis for all field orientations. Using a two-band/two-gap model to calculate the magnetization, we are able to fit our results yielding a penetration depth anisotropy, ${\ensuremath{\gamma}}_{\ensuremath{\lambda}}=1.1\ifmmode\pm\else\textpm\fi{}0.1$.

Using small-angle neutron scattering we have studied the magnetic flux line lattice in YNi2B2C with the field rotated 30° away from the crystalline c-axis. Previously we have reported on a square to hexagonal symmetry transition of the flux line lattice below 1 kOe for H|c . We find that the rotation of the field shifts the transition to higher fields in agreement with theoretical prediction. Two different directions in the ab-plane were chosen as axes of rotation. Rotating the field around [1,1,0] shifts the onset of the transition up to 3 kOe. Rotating the field around [1,0,0] stabilizes the hexagonal flux line lattice up to the highest measured field of 30 kOe. The difference between the two axes is also reflected in the flux line lattice distortion.

MAGNETISM and superconductivity are manifestations of two different ordered states into which metals can condense at low temperatures. In general these states are mutually exclusive1; they do not coexist at the same place in a sample. The study of the interplay between these properties has recently been revitalized by the discovery2,3 of a class of compounds with formula RNi2B2C (where R is a rare-earth element) which are both antiferromagnetic and superconducting at sufficiently low temperature4. It has been suggested5 that magnetic and superconducting order can coexist in these materials on an atomic scale. Here we use small-angle neutron scattering to study the structure of the superconducting vortex lattice in ErNi2B2C. Our results show that the development of magnetic order causes the vortex lines to disorder and rotate away from the direction of the applied magnetic field. This coupling of superconductivity and magnetism provides clear evidence for microscopic coexistence of magnetic and superconducting order, and indicates that magnetic superconductors may exhibit a range of unusual phenomena not observed in conventional superconductors.

We present a $(B,T)$-phase diagram of the magnetic superconductor ${\mathrm{TmNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ obtained by neutron scattering. The measurements were performed in magnetic fields up to 6 T applied along the crystalline a axis. The observed phases are characterized by three ordering vectors, ${\mathbf{Q}}_{\mathrm{F}}=(0.094,0.094,0),{\mathbf{Q}}_{\mathrm{AI}}=(0.483,0,0),$ and ${\mathbf{Q}}_{\mathrm{AII}}=(0.496,0,0),$ all with the magnetic moment along the c axis. In zero and low fields the Tm $4f$-moments order in a long wavelength transverse spin density wave with $\mathbf{Q}={\mathbf{Q}}_{\mathrm{F}}.$ The magnetic ${\mathbf{Q}}_{\mathrm{AI}}$ structure is stabilized by an applied field of 1 T and a transition to ${\mathbf{Q}}_{\mathrm{AII}}$ is observed at 4 T. For both transitions there is a broad temperature and field range of overlap between the different states. Surprisingly, we observe that the ${\mathbf{Q}}_{\mathrm{A}}$ phases persist to increasingly higher temperatures when the field is increased. Doping with Yb has been introduced to partly suppress superconductivity. In $({\mathrm{Tm}}_{0.90}{\mathrm{Yb}}_{0.10}){\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ the ${\mathbf{Q}}_{\mathrm{F}}\ensuremath{\rightarrow}{\mathbf{Q}}_{\mathrm{AI}}$ phase transition is also observed but at a larger transition field compared to the undoped compound. In $({\mathrm{Tm}}_{0.85}{\mathrm{Yb}}_{0.15}){\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ the ${\mathbf{Q}}_{\mathrm{F}}$ phase persists up to at least 1.8 T. The magnetic correlation length of the ${\mathbf{Q}}_{\mathrm{AI}}$ phase in ${\mathrm{TmNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ measured parallel and perpendicular to the magnetic field, is constant within 10% at all fields and temperatures.

We have performed scanning tunneling spectroscopy imaging of vortices in ${\mathrm{MgB}}_{2}$ with both the tunneling current and the applied field perpendicular to the crystalline c axis. This revealed a well ordered vortex lattice with a relatively low anisotropy of $1.19\ifmmode\pm\else\textpm\fi{}0.04.$ This is significantly below the upper-critical-field anisotropy, but in good agreement with theoretical predictions for the penetration depth anisotropy, which at low fields is expected to be dominated by the $\ensuremath{\pi}$ band. The value of the anisotropy is smaller than estimated from small-angle neutron-scattering measurement.

Using small-angle neutron scattering, we have imaged the magnetic flux line lattice (FLL) in the d-wave heavy-fermion superconductor CeCoIn5. At low fields we find a hexagonal FLL. Around 0.6 T this undergoes what is most likely a first-order transition to square symmetry, with the nearest neighbors oriented along the gap node directions. This orientation of the square FLL is consistent with theoretical predictions based on the d-wave order parameter symmetry.

We present neutron scattering from the flux line lattice (FLL) in MgB2. Between 0.5 and 0.9 T the FLL undergoes a 30 degrees reorientation, and simultaneously the scattered intensity falls sharply consistent with the weaker superconducting pi band being suppressed with increasing field. We speculate that the pi and sigma bands favor different FLL orientations, and that the reorientation is driven by the suppression of the pi band. When the c axis of the crystal is rotated 45 degrees to the applied field the penetration depth anisotropy could be measured, and rises both as a function of applied field and temperature.

Spanning a broad range of physical systems, complex symmetry breaking is widely recognized as a hallmark of competing interactions. This is exemplified in superfluid 3He which has multiple thermodynamic phases with spin and orbital quantum numbers S = 1 and L = 1, that emerge on cooling from a nearly ferromagnetic Fermi liquid. The heavy fermion compound UPt3 exhibits similar behavior clearly manifest in its multiple superconducting phases. However, consensus as to its order parameter symmetry has remained elusive. Our small angle neutron scattering measurements indicate a linear temperature dependence of the London penetration depth characteristic of nodal structure of the order parameter. Our theoretical analysis is consistent with assignment of its symmetry to an L = 3 odd parity state for which one of the three thermodynamic phases in non-zero magnetic field is chiral.

We report scanning tunneling spectroscopy imaging of the vortex lattice in single crystalline MgB2. By tunneling parallel to the c-axis, a single superconducting gap (Delta = 2.2 meV) associated with the pi-band is observed. The vortices in the pi-band have a large core size compared to estimates based on Hc2, and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. These results suggest that superconductivity in the pi-band is, at least partially, induced by the intrinsically superconducting sigma-band., Comment: 4 pages, 3 figures

When a type-II superconductor is placed in a magnetic field, it is threaded by swirling whirlpools of electric current known as vortices. The vortices behave like massive entities and provide a unique probe into the nature of the superconducting state in the host material. Furthermore, the collective vortex behavior is of crucial importance for practical applications since vortex motion will lead to dissipation. I will discuss two recent vortex lattice (VL) studies using small-angle neutron scattering (SANS) that exemplify the continuous evolution of this technique. In the first example we used SANS to determine the superconducting anisotropy of Sr2RuO4 (SRO) that is among the few superconductors believed to exhibit p-wave pairing [1]. While there is significant experimental support for unconventional pairing, there is a discrepancy between the anisotropies of the upper critical field and the Fermi surface. Taking advantage of the significant transverse VL field component that arises due to the large anisotropy of SRO we measured the superconducting anisotropy ≍ 60, roughly three times greater than the upper critical field anisotropy. This result imposes significant constraints on possible models of triplet pairing in SRO. In the second example we used a stop-motion technique to study VL transition dynamics in MgB2 [2,3]. Here the VL exhibit extensive metastability in connection with a second order rotational phase transition that cannot be understood based on the single VL domain free energy or vortex pinning. Instead, we have proposed that a jamming of VL domains acting as granular entities is responsible for the metastability. We have performed extensive SANS experiments, as the VL is driven from the metastable to the ground state by small-amplitude AC magnetic field oscillations. This shows a dual power-law behavior indicating a two-step process for the transition to the ground state. Supported by the US Department of Energy (Grant No. DE-FG02-10ER46783).

We review the results of neutron diffraction studies on both the superconducting flux line lattice (FLL) and the ordered magnetic state in TmNi2B2C, in order to study the interaction between magnetism and superconductivity in this compound. With an applied magnetic field along the direction of the ordered moments parallel to crystalline c-axis, we found that the magnetic order and the FLL undergoes a simultaneous phase tran

We review the results of small neutron scattering studies of the superconducting flux line lattice (FLL) in the borocarbide RNi2B2C superconductors. The first experiments on these compounds with magnetic field parallel to the c axis discovered a square FLL in the majority of the phase diagram, with a smooth transition to a hexagonal symmetry at field below ~ 1 kOe. These results proved to be in agreement with the predictions of a model by V. Kogan et al. which includes non-local corrections to the London model due to the Fermi surface anisotropy of the borocarbides. A very different transition is observed when the applied magnetic field is perpendicular to the c axis. In this case, a discontinuous reorientation between two hexagonal vortex arrangements is observed at a well defined line in the magnetic phase diagram.

We have measured the structure of the field cooled flux line lattice (FLL) in single crystal Nb using small angle neutron scattering. Augmented by transport and thermodynamic data, a scenario for the dramatic disordering of the FLL near the peak effect emerges. A precursor to the peak effect is an hexatic FLL as positional order is lost. As the critical current rises, the orientational and longitudinal correlation lengths also fall, leading to an amorphous array of lines at the critical current maximum.

The two-gap structure of MgB 2 gives rise to unusual thermodynamic properties which depart markedly from the single-gap BCS model, both in their temperature- and field-dependence. We report measurements of the specific heat up to 16 T on ceramic and single crystal samples, which demonstrate these effects in bulk. The low-temperature mixed-state specific heat reveals a field-dependent anisotropy, and points to the existence of unusually large vortices, in agreement with local density-of-states measurements by scanning tunneling spectroscopy. It is finally shown that a suitable irradiation process nearly doubles H c2 in the bulk.

We report on the results of scanning tunneling spectroscopy measurements on single crystals of MgB 2 . Tunneling was performed parallel to the crystalline c -axis, and a single superconducting gap ( Δ π =2.2 meV) associated with the π-band is observed. Vortex imaging in the π-band was performed with the field parallel to the c -axis. The vortices are found to be organized in a well-ordered hexagonal lattice.

We present small-angle neutron scattering (SANS) studies of the superconducting vortices in Ba(Fe0.93Co0.07)2As2. A highly disordered vortex configuration is observed up to the highest measured field of 3 T. The field dependence of the magnitude of the SANS scattering vector indicates small vortex lattice domains of rhombic symmetry or a vortex glass with short-range hexagonal order. The disordering is attributed to strong single-vortex pinning. This is supported by an analysis of the radial width of the intensity distribution, which indicates a correlation length of a few vortex spacings. Measurements of the scattered intensity are found to decrease with increasing magnetic field, consistent with theoretical models and in reasonable agreement with estimates of the upper critical field. The temperature dependence is found to follow the BCS s-wave prediction.

From small-angle neutron scattering studies of the flux line lattice (FLL) in CeCoIn5, with magnetic field applied parallel to the crystal c-axis, we obtain the field and temperature dependence of the FLL form factor (FF), which is a measure of the spatial variation of the field in the mixed state. We extend our earlier work (Bianchi et al 2008 Science 319 177) to temperatures up to 1250 mK. Over the entire temperature range, paramagnetism in the flux line cores results in an increase of the FF with field. Near Hc2 the FF decreases again, and our results indicate that this fall-off extends outside the proposed Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) region. Instead, we attribute the decrease to a paramagnetic suppression of Cooper pairing. At higher temperatures, a gradual crossover toward more conventional mixed state behavior is observed., New Journal of Physics, 12, ISSN:1367-2630

Using small-angle neutron scattering we have studied the flux line lattice and the magnetic structure in TmNi2B2C. With an applied field parallel to the crystalline c-axis several magnetic and flux line lattice symmetry transitions have been reported. The subject of this paper is the field-induced magnetic structure and how it is influenced by the flux line lattice symmetry. We find that the domain splitting of the field-induced magnetic structure is hysteretic, and appears to be determined by the history of the flux line lattice symmetry.

In this work we present a corpus for the evaluation of sensitive information detection approaches that addresses the need for real world sensitive information for empirical studies. Our sentence corpus contains different notions of complex sensitive information that correspond to different aspects of concern in a current trial of the Monsanto company. This paper describes the annotations process, where we both employ human annotators and furthermore create automatically inferred labels regarding technical, legal and informal communication within and with employees of Monsanto, drawing on a classification of documents by lawyers involved in the Monsanto court case. We release corpus of high quality sentences and parse trees with these two types of labels on sentence level. We characterize the sensitive information via several representative sensitive information detection models, in particular both keyword-based (n-gram) approaches and recent deep learning models, namely, recurrent neural networks (LSTM) and recursive neural networks (RecNN). Data and code are made publicly available.